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Troubleshooting Alternator and Charging System Problems

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

The alternator is at the heart of the charging system of your vehicle.

The alternator is at the heart of the charging system of your vehicle.

Alternator problems and charging system problems can affect your vehicle in different ways. You may notice:

  • your ALT or CHARGE indicator light comes on,
  • your engine is hard to start and cranks slowly, or doesn't crank,
  • your battery demands lots of water,
  • your alternator makes noises,
  • or your headlights suddenly go dim.

These and other problems may be caused by a fault in the charging system.

Before you start replacing components with the hope of fixing the problem, you need to determine which component or components are causing you trouble. Often, it is possible to diagnose and solve the problem on your own using a few simple tests and tools.

The sooner you find out what is causing trouble, the better. You'll prevent a faulty component from ruining other parts in the system, which would make your repair more expensive.

This convenient troubleshooting guide will help you find out what you need to know, using a few simple checks you can do at home using a test light or digital multimeter (DMM) and possibly a few other common tools.

It is a good idea to have on hand the vehicle repair manual (or a good aftermarket manual) for your particular car make and model. It will help you identify wires, specific components, and possibly suggest some specific tests recommended by your manufacturer.

If you want to test the condition of the system as a diagnostic starting point, do the tests described in the following section, "General Charging System Check."

However, if you need help for a specific problem with your charging system—for example, an over-charge or under-charge condition, discharging battery, or noisy system—then skip over to the "Charging System Problems and Potential Causes" section.


I. Common Symptoms of a Bad Alternator or Charging System

II. General Charging System Checks

III. Charging System Problems and Potential Causes

IV. Troubleshooting for Unusual Voltage System Drops

The battery indicator should turn off when your engine is running.

The battery indicator should turn off when your engine is running.

I. Common Symptoms of a Bad Alternator or Charging System

Indicator Light On

Usually, the first sign that your charging system is in trouble is a "battery," "ALT," or "CHARGE" warning light illuminating on your instrument panel while driving. It means that the alternator voltage output is below 12 volts, or over its limit or has stopped charging the battery and your car is running on battery power.

If the light illuminates only intermittently, it usually indicates a loose or worn drive belt or serpentine belt, worn-out or bad carbon brushes in the alternator. But remember that the light doesn't always mean there is a bad part; the light may be triggered by a sensor giving a wrong message or there's something wrong with the circuit itself.

Engine Cranks Slowly, Doesn't Crank or Stalls

When the battery is undercharged, you may have difficulty starting the vehicle, the engine cranks slowly or doesn't crank at all. Also, the engine may stall if the alternator can't produce enough power to run the ignition system. Go over the next section on "General Charging System Checks," and, if necessary, check the section "IV. Troubleshooting for Unusual Charging System Voltage Drops." further down in this article.

Battery Overheating and Using Too Much Water

An overcharged battery causes the battery to overheat. You find yourself adding water to the battery frequently. If the problem is not taken care of on time, it can ruin your battery. Besides going through the next section, make sure to check section IV below on "Troubleshooting for Unusual Charging System Voltage Drops"

Noises Under the Hood

Squealing, buzzing or grinding noises coming from the engine may be caused by bad alternator components, a loose or worn-out serpentine belt, or a faulty belt tensioner, loose alternator pulley or mounting bolts, worn bearings, or faulty diodes. See the "Checking for Alternator Noises" subsection further down in this article.

Dimming Lights

If you notice the headlights, instrument panel, or interior lights dimming or flickering, power windows running slow, radio or gauges don't operate as they should, either your battery has a low charge, or there's one or more faulty diodes inside the alternator. Check your battery and see the "Alternator AC Voltage Leak Check" subsection further down in this article.

Check the drive belt for adjustment and tensioner for proper operation.

Check the drive belt for adjustment and tensioner for proper operation.

II. Six Tests for the Charging System in General

These series of charging system checks help diagnose the general condition of your charging system. They can help you confirm that you actually have a problem in your charging system and locate the source of the problem.

1. Make a Visual Inspection of the System

With the engine off, pop the hood open and visually inspect the different components of the charging system. Look for a worn out or loose drive belt, alternator connection problems, loose alternator mounting bolts, and corrosion and dirt around the battery case and cables.

When inspecting the drive belt, check for adjustment. If necessary, adjust the belt with the help of your car owner's manual or repair manual. Inspect the belt for signs of cracks, cuts, shiny spots, deterioration or other signs of wear or damage. Change the belt and belt tensioner at the manufacturer's recommended interval.

2. Check for Wiring Problems

Inspect the wires and connections at the back of the alternator, at the remote voltage regulator (if applicable), and at the battery. Look for corrosion at the connectors, damaged wires, and burned and missing insulation that might suggest an electrical short.

3. Do This If the Indicator Light Stays On, or Goes On and Off

Follow the next steps:

  • Start the engine and apply the emergency brakes. Set the transmission to Neutral (manual) or Park (automatic).
  • Connect a voltmeter across the battery terminals.
  • While watching the voltmeter display, start wiggling wires at the back of the alternator, the battery, and the remote voltage regulator (if there is one).
  • If the voltage reading on the meter display goes up while wiggling one of the wires, you've found a bad electrical wire or connection.

Instead of using a voltmeter, you can have an assistant watch the indicator light on the instrument panel to see if it turns off as you wiggle various wires and connectors. Once the light turns off, you've found the problem connector or wire.

4. Check for Alternator Noises

Bad alternator bearings, rectifiers, rotor shaft, stator winding, slip rings, brushes and other parts inside the alternator with mechanical or electrical problems can become noisy.

Here's a test you can do: Use a length of vacuum hose to listen for alternator noises. The hose will amplify the noise if it's coming from the alternator. But be very careful around moving parts while you do this test.

  • Start the engine.
  • Place one end of the hose against your ear and move the other end around different points of the alternator body.
  • Listen for whining noises (this can indicate a bad diode or an over-charging condition), grinding (bad bearing), squealing, or other abnormal noise. If necessary, have your alternator checked.

5. Check for Under-Charging and Over-Charging

The next three tests are best done using a load tester, but you still can use your digital voltmeter. You do this by measuring system voltage while loading the system.

5a. First, measure battery base voltage to make sure you have a fully charged battery.

  • Turn on the high beams for 10 seconds and then turn them off.
  • Wait for two minutes
  • Measure battery voltage across the battery posts with your DMM. You should get between 12.4 and 12.6V. This means your battery is fully charged. If you get a reading below 12.4V, charge the battery before continuing.

5b. Measure the Charging System's No-Load Voltage

  • Ask an assistant to start the engine and hold engine speed at about 1500 RPM.
  • Measure voltage across the battery with your DMM. You should get 0.5 to 2 volts higher than base voltage. If you are getting more than 2 volts above base voltage, most likely your alternator is over-charging the battery or the battery is faulty. Other potential problems are a faulty voltage regulator or a problem in the charging system wiring. As part of your wiring checks, see the section "Troubleshooting for Unusual Charging System Voltage Drops" below.

5c. Measure charging system load voltage with a high-current-condition system measurement.

  • Ask an assistant to start the engine and hold engine speed at about 2000 RPM. Turn on all electrical accessories like A/C, blower motor, headlights, defroster, wipers. But don't turn on the heated windshield if your vehicle has one; alternator voltage may increase to over 100V and this can be unsafe.
  • Take a voltage reading across the battery posts. Your reading should be at least 0.5 volts above base voltage for your system to keep up with electrical system demands. Otherwise, the charging system can't meet the demand and charge your battery. This fault could point to a faulty alternator or voltage regulator. Check the section "Troubleshooting for Unusual Charging System Voltage Drops" below to check for wiring problems that can lead to this condition.
  • NOTE: These measurements correspond to an ambient temperature of about 70º F. The charging voltage will increase as temperature drops, and charging voltage will decrease as temperature goes up. So keep this in mind when making your measurements.

6. Check for Alternator AC Voltage Leak

Alternators use diodes to rectify alternating current produced by the alternator into direct current. When one or more diodes go bad or a stator winding fails, the alternator can cause all kinds of problems. AC voltage leak can cause your lights to dim and drain power from your battery, for example. Usually, you can detect this leak by measuring AC voltage at the alternator.

  • Start and let the engine idle.
  • Set the parking brake and your transmission to Park (automatic) or Neutral (manual).
  • Set your meter to a low AC voltage range.
  • Ask an assistant to increase engine RPM to 2000 rpm.
  • Touch the red meter lead to the alternator battery terminal B+.
  • Touch the black meter lead to the alternator case (ground).
  • If your DMM reads 0.4 AC volts or less, the diodes are good.
  • If your DMM reads 0.5 AC volts or more, the diodes or stator is faulty.

Once you've determined the condition of the system, you can go over the next section to zero in on the potential problem(s) that may be causing the condition of the charging system.

A single bad battery cell can prevent your charging system from working properly.

A single bad battery cell can prevent your charging system from working properly.

III. Charging System Problems and Potential Causes

To speed up your diagnosis and repair, look up the system condition that most resembles your problem and go over the potential causes described under that condition. Some checks or tests may be suggested as appropriate.

1. If the Battery Seems to Stay Undercharged

You have already charged your battery a couple of times and you just found out the battery is undercharged again. Before you blame your battery, or the alternator, here are some preliminary checks you may want to do.

a) Check the drive belt or serpentine belt, especially if you haven't replaced it in the last five years. Make sure the belt has the proper tension. Look for signs of wear or damage like cuts, shiny spots, missing chunks. Today serpentine belts don't show signs of wear, even if they need to be replaced. Use a belt wear indicator or check your maintenance schedule for the replacement interval suggested by your car manufacturer. You may find the schedule in your car owner's manual or your repair manual.

b) Along with the drive belt, check the belt tensioner as well. Make sure it turns freely and is noise-free. Car manufacturers recommend replacing the tensioner at the same time you replace the drive belt.

c) Make sure your battery connections are tight and clean. However, just because the terminals look clean, it doesn't mean they are tight and in good condition. Look for damage to the cable and the terminal itself that may prevent proper electrical current flow.

d) Check your battery yourself, or take it to your local auto parts store. Many of these stores will test your battery for free.

e) There's a parasitic battery drain stealing power from your battery.

  • A quick test is to connect a test light in series between the positive battery cable and the positive battery post. If the test light comes on, there is an electrical drain in one of the systems.
  • First, unplug the alternator electrical connector. If the test light goes out, the alternator is causing the drain. If not, locate the parasitic drain.

f) Don't overlook the starter motor: a failing starter motor may draw excessive current during operation, draining battery power. If necessary, have your starter motor or starting system tested.

g) If you recently added an electrical accessory to the vehicle, you may have over passed your alternator's capacity.

h) There could be an alternator wiring problem.

i) Have the alternator and battery checked.

2. If the System Seems to Be Over-Charging

Besides test results, another potential sign that your battery is being overcharged is that your battery terminals keep accumulating corrosion.

Here are some checks you want to do:

  • Make sure that all the connections to the alternator, remote voltage regulator (if applicable) and battery are clean, tight and in good condition.
  • Check your battery or have it tested at your local auto parts store. A bad battery cell can cause the alternator to over-charge the good battery cells.
  • Check for a bad alternator voltage regulator and circuit. Consult your vehicle repair manual, if necessary.
  • Make sure you have good ground connections at the alternator (alternator case) and voltage regulator, especially if your vehicle uses a remote voltage regulator. Grounds should be free of rust, and the alternator and remote voltage regulator mounting bolts should be clean and tight.
  • Check the alternator rectifier or have your alternator checked at the auto parts store.
  • Also, conduct the tests described in the Troubleshooting for Unusual Charging System Voltage Drops below.

3. If the Alternator Is Not Charging the Battery

When your tests point to an under-charge or no-charging condition:

  • Make sure the drive belt is not loose or worn out.
  • If necessary, borrow a good battery just to operate the engine and confirm that your drive belt and belt tensioner are operating properly.
  • Manually check the belt tensioner for proper operation. Make sure the tensioner pulley turns freely and without noise. Check it for damage.
  • Manually turn the alternator pulley and make sure it turns without a problem. If one of the bearings has seized, it won't allow the alternator to turn freely.
  • Check that the connections at the battery, alternator, and remote voltage regulator are clean and tight.
  • Check for a blown fuse or fusible link. Consult your vehicle repair manual, if necessary, to locate the alternator fuse or fusible link.
  • Do the tests described in the section "Troubleshooting for Unusual Charging System Voltage Drops" below.

4. If the Engine Makes Noises

Noise can be a sign of alternator problems when it comes from the charging system. The next checkpoints will help you isolate the source of the noise.

  • Check the drive belt or serpentine belt. Look for signs of wear or damage like cuts, shiny spots or missing chunks under the belt. A worn out belt can squeal during operation.
  • Also, check the belt tensioner for proper operation and damage. It should rotate freely.
  • Make sure the alternator is properly mounted. Loose mounting bolts can cause the alternator drive belt and drive pulley to become misaligned and noisy.
  • Check the alternator for noises. See the General Charging System Checks section for a simple procedure for this.

5. If Lights Dim During Engine Operation

Most alternators use diodes inside a rectifier to turn Alternating Current (AC) into Direct Current (DC) for use by the system. When one or more diodes go bad, AC can leak into the electrical system. Sometimes you can notice this when the headlights, instrument panel lights, and other interior lights dim during engine operation. To test your alternator for AC current leaks, see the Alternator AC Voltage Leak Check subsection in the previous section.

Measure system voltage and drop voltages using a digital multimeter.

Measure system voltage and drop voltages using a digital multimeter.

IV. Troubleshooting for Unusual Charging System Voltage Drops

A charging system voltage drop check can help you locate the source of an under-charge or over-charge condition due to problems in the wiring or connections between the battery and alternator.

1. Start the engine and let it idle. Apply the parking brake and set the transmission to Neutral (manual transmission) or Park (automatic transmission).

2. Turn on the high beams to provide a system load. And have an assistant raise engine speed to about 1500 RPM. If your vehicle is equipped with a heated windshield, don't turn it on; this can make alternator voltage go over 100 V. Since you'll be working around alternator connections, this could be dangerous.

3. With your voltmeter test leads, touch the positive battery post and the B+ terminal connector at the back of the alternator.

4. Check your meter display. You should get around 0.4V or less of voltage drop. If your voltage drop is higher, it can lead to an under-charge condition. Check the connections in that part of the circuit for a loose wire, corrosion at the connectors or wiring damage that may prevent proper current flow between the battery and alternator. Also, check the electrical connections at the back of the alternator and at the voltage regulator.

5. Now repeat the test, but this time, connect your meter leads between the battery negative post and the alternator case.

6. Check your meter display. Again, you should get a voltage reading around 0.2V or less. If your voltage drop is higher, there's something wrong. This can lead to an over-charging condition. Checking that part of the circuit, make sure the battery ground connection is good, clean and tight. Add a temporary ground connection from the battery to the chassis. If this removes the high voltage drop, check the engine to body grounds connections. They should be clean, tight and in good condition.

Watch the next video for a visual reference on voltage drop checks.

Alternator problems are not uncommon after a few years of operation. A typical alternator may last anywhere from 8 to 12 years. So don't be surprised to find your alternator going bad or the system developing problems after a few years of trouble-free operation, even if you have maintained your car well.

The key point here is to do the proper diagnostic as soon as possible because a bad alternator can ruin an otherwise good battery, and other components as well, depending on the fault.

Once you determine that your alternator is bad, you have several options. You can replace it with an original one from your dealer, an aftermarket replacement, or a rebuilt unit. Aftermarket alternators are a good option and less expensive, and many of them are just as good as their OEM counterparts. And rebuilt alternators are not as bad either. So consider your options.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: I have a 2005 Ford Taurus one day it wouldn’t start. It finally started and flashing lights to check the brake system in the charging system, but then it wouldn’t start once it was jumped. It kept stalling, so we had it checked at an auto parts store. They agreed alternator replaced the alternator and it is still doing the same thing do you have any idea what else could be wrong?

Answer: Check all the grounds -- battery to body and body to engine. They should be clean and tight. Bad grounds can eventually, damage the alternator. Test for voltage drop on the grounds, battery and charging system.

Question: I have a 2011 Mazda 3, 2.5. The battery light turned on when I was driving at 120 km/h and would turn off if I slowed down. The light now starts at 90 km/h and will turn off if I slow down (maybe rpm related, not sure). Battery, alternator and start engine were tested at the dealership but seem to be OK. The battery seems to slowly drain within a few weeks as the speed decreases for the battery light to turn on. What could it be?

Answer: This may be an alternator issue with worn brushes, slowly losing the ability to charge the battery. A common test is to replicate engine rpm at which the light comes on. Watch the engine rpm when the battery light comes on. At home, with the transmission in Neutral or Park, increase engine speed to the same rpm and see if the light comes on. If it does, the alternator needs new brushes.

Question: My alternator doesn't charge for around 3 to 4 km of driving in the morning. Then it starts working perfectly throughout the day, what can be the cause?

Answer: You may have a bad connection. Have the alternator checked to make sure it is working properly? Test the circuit voltage drop and, if necessary, engine grounds. These other two posts can help:



Question: On my way home, the alternator light came on but made it home fine. The next day, the truck was hard to crank and would only stay running if my foot remained on the gas. The next day, I charged the battery and put it back in. Thought it was fixed but now the battery is dead and won’t recharge. What’s the problem now?

Answer: Have the battery and alternator checked. If the alternator or charging system was faulty, it could've damaged the battery. Also checking the charging system voltage drop may help in the diagnosis.


Question: I have a 2001 Toyota Solara with 158,000 miles. I've gone through 5 alternators in about 6 yrs. Even the Toyota oem. Two reliable mechanics can’t figure it out. I’m taking it to a shop that specializes in electrical problems. Do you have any ideas?

Answer: Knowing how the previous alternators failed can give a clue about the type of issue you are dealing with (electrical, mechanical). Usually when alternators failed prematurely is because of a bad battery (electrical), voltage regulator issues, high electric loads (e.g. running AC fan at high) or a drive belt that is putting unusual stress on the alternator pulley (mechanical)(make sure the belt is not too tight). Alternator quality can be another factor of course.

Check for signs of fluid leakage around the alternator that might affect the stator or rotor or both.

Question: I have a good alternator, but my battery runs down. It passed tests performed at two auto parts stores. When this problem occurred, I was able to get home by starting the vehicle (2000 GMC Yukon, 5.3L) by disconnecting the battery. Voltage when up close to 14 according to the gauge. When I reconnected the batter at home, it was still dead. Got a new battery and have the same problem with battery drain. Do you have any ideas?

Answer: If you have some power amplifier, or some other power accessories, this could be running down the battery if the alternator can’t keep up with the demand. Other than that, you may want to have the alternator checked in a shop, and see where the charge is going while the engine is running.

You can check for a parasitic drain that you may not be aware of. This post can help you:


Question: I installed a new 105-amp alternator in my 1982 Chevrolet C10. When I start the engine, it indicates 14.6 volts on the voltmeter connected to the battery. When I start the AC fan and the AC compressor, the voltage increases to 15.8 volts. After a while, the alternator stops charging; I think it might be defective. I changed two alternators, but I still have the same problem. What do you think?

Answer: Check the voltage regulator and the battery. An auto parts store may check the battery for you. Also, may sure the circuit connections for the charging system are clean and tight and check the engine body grounds.

Question: I have a 2004 Taurus, and I've changed the battery and alternator but the charging system light is still on. Any ideas why?

Answer: Check the fusible link, you can test it with your multimeter.

Question: I got a 2012 Nissan Xterra. I just installed a new alternator and new battery. It starts up good and idles good now as well, but when I give it full throttle and get close to 3,000 RPMs, my battery light and park brake lights comes on and flashes at me. And the battery volt gauge goes down a whole lot. What could be the problem?

Answer: Check the alternator belt and tensioner. Belt should have the proper pressure. If it's loose, it won't charge properly during hard accelerations. Check voltage at the battery when accelerating (at idle and emergency brakes applied). You should get around 13.5 or so. Otherwise, there could be a problem with the voltage regulator. You may need to replace the alternator. If not, check the wires and connections between the battery and alternator.

Question: I had my alternator rebuilt. Now I am having a problem getting it to charge at idle, I get 14.5 volts at 1500 rpm, but as soon as I release the throttle it drops down to battery voltage, I've returned the alternator once already. He checked it again, replaced the regulator and said it's putting out full voltage, but on the car, it's doing exactly as I mentioned before, no voltage at idle, full voltage when revving the engine. Could this be a PCM issue?

Answer: Check the belt and belt tensioner for the correct tension. Take a look at the connections at the back of the alternator, especially the B+ connector. On early models the indicator light on the dashboard should come on when the ignition key is in the On position, otherwise, you'll have problems at idle. There could also be a problem in the charging circuit, a loose, corroded or damaged wire can also prevent full voltage at low rpm. Take a look at the grounds and the output wiring to the battery. You may need the diagram for this. These other posts may help:



Question: Battery tested fine, but alternator voltage would go up and down. Occasionally, a BATTERY SYSTEM FAILURE light will come on. Could it be a sensor/fuse problem since it doesn’t stay on all the time?

Answer: The alternator could be faulty. But you may want to run a voltage drop test on the circuit first. Some models, like GM, have a fusible link in the circuit. Make sure that it’s good. This other post has a voltage drop section that may help:


Question: My voltage is fine when I start the vehicle, but after driving around for about 10-15 minutes, my voltage goes from 14v to 15.5-16v. I have an aftermarket voltage regulator, and a high output 320 amp alternator and my battery dies if I don’t unhook the wire from my battery to the cars fuse box. Do you have any ideas?

Answer: You need to make sure the alternator is suited for your application. These alternators need the right pulley ratio and pulley diameter to work correctly. Also check that it has the right size battery cables hook to the battery.

Question: Our engine will take too much time to start. How can I check the alternator?

Answer: The problem might be with the battery, starting system, ignition or fuel system. Check the batter condition, check for spark and fuel pressure.

Question: I have a Toyota Corolla VVTI model 2004, I have changed the alternator but the battery indicator is still present. I have checked the fuses and connections, but the problem continues. What could be the issue?

Answer: Have the battery tested, and check the connections in the charging system. Make sure they're clean and tight. Also, the check the engine grounds.

Question: I put my OBDll reader on my car and it says my charging system output is high. What does that mean exactly?

Answer: This basically means the alternator is overcharging the battery. Usually the problem here is the voltage regulator. Before replacing the alternator, you can take the alternator to a local auto parts store and have them check it for you. Make sure the alternator is the problem.

Question: What are the most common faults likely to occur in a charging system? More than 6 points at least.

Answer: There can be a problem with the circuit, voltage regulator, ignition switch, corroded battery cables, faulty battery, worn or loose drive belt, bad car computer.

Question: I have a 1998 Ford Mustang. I’ve changed the battery and the alternator. I’m still losing voltage from the alternator to the battery. It is just running on the battery. What can cause this problem?

Answer: You might want to make a voltage drop test on the charging circuit. There could be a bad connection or wire that is not too evident. This other post will give you an idea on how to go about the test:


Question: I replaced the original alternator on my 2015 Kia Forte. The replacement alternator shows that it went bad and that I replaced it with the second one, now it went down. What is the problem? I have also noticed the positive battery post on my battery gets hot. Do you have any idea what it could be?

Answer: There could be too much resistance on that side of the circuit. Check the cable for damage, or a problem at the connectors. If everything seems okay, have your battery tested.

Question: I have a 2003 VW Eurovan. Recently, the ABS light went on, then, after a few minutes the regular red brake light lit and the car stopped. What is going on?

Answer: You need to download the trouble codes. There could be a number of things that triggered the ABS light - problems with the tone ring, wheel bearing, speed sensor (and wiring).

Question: I have a 06 Mustang GT. I replaced the alternator because it was causing a camshaft position sensor code. After replacing it and checking my work, the battery light with a warning "check charging system" comes on. It comes on for a minute or so then goes out for a few minutes. The battery seems to stay around 13.7 volts what could be causing the light to come on randomly? I have not driven it yet.

Answer: Check the circuit connections. This could be a loose or bad wire/connector. You may want to try a voltage drop test. This post gives you an idea of the test:


Question: I have a 2014 Nissan Pathfinder. I changed my alternator in July 2018. Alternator stopped working again on 2/6/2019 and replaced it on 2/7/2019. Back in the shop on 2/11/2019 with bad alternator again. This time the alternator is overcharging. The alternators were bought from O'Reilly's auto parts. Just found out they are rebuilt alternators, and not new. Still, the price was $400 for the part. Could there be something causing the part to go bad so quick or could it just happen to be bad parts?

Answer: Make sure you are using the correct battery for your application. On some newer models using the incorrect battery can affect the alternator, especially those that interact with the ECU. Also, check the belt and pulleys. Make sure the pulleys are correctly aligned, and the alternator is properly mounted without rust accumulation, especially the ground connections, including engine and battery grounds. Also, check the wiring for signs of electrical faults. And yes, some models are very sensitive to using parts other than OEM, but first, make the previous checks.

Question: What would cause my alternator to be charging where it supposed to be, then cause it to drop all of the sudden? You can barely tap it and it goes back up.

Answer: Probably you are dealing with an alternator with worn brushes. Tapping the alternator shake the brushes a bit and help them make better contact or the copper wires connected to the brushes are damaged.

Question: I have a 2012 Town and Country with 110k miles. Last year at around a 100k miles I replaced the alternator due to regulator failure. This year I installed a new battery. The problem is the charging light comes on randomly. I drive around with a voltmeter to run these tests the moment it happens, but everything checks out. Why does the light come on and not go out?

Answer: Check the belt. A worn belt may slip intermittently, affecting the charging system. The problem with newer belts is they look good even if they are worn. Check the belt for tension and wear (use a belt wear gauge), tensioner, pulleys, and grounds, and especially engine grounds.

Question: What causes voltage to fluctuate?

Answer: There could be several causes behind the issue:

bad alternator, bad voltage regulator, bad connections between the battery and alternator.

First, make sure the connections are clean and tight, and the cables are good. Especially, check the grounds between the engine and body. Then, have the alternator tested in your local auto parts store.

Question: I have a 1966 Ford Mustang and have swapped out the alternator 3 times. It will work fine at times, then at other times the voltage steadily drops, especially if I turn the lights on. The belt is good, connections are good. The battery is good. Any ideas as to what the problem could be?

Answer: Make sure you have clean and tight connections to the voltage regulator. If necessary, have the regulator checked. it might not be sensing the voltage drop at the alternator when load increases. And the battery doesn't get the required charge. Hope this helps.

Question: I have an 04 Lincoln aviator. I changed the battery, alternator and I am still getting a check charging system message. What do I do next?

Answer: Make sure you actually have a charging problem. Your local auto parts store can check the alternator and battery for you. If there's a problem, it could be in the circuit. If not, the circuit for the warning light might be the issue.

Question: I have a GM 3500 6.0 with an overcharging problem. I ran new wires to the PCM and fuse box for the connector. I have a brand new alternator, PCM, and ACDelco battery. The power wire for the alternator to the battery reads correctly as well. But it is still charging to 15.6-16.0. What could possibly be going wrong with my car's alternator?

Answer: The problem could be on the ground side of the circuit. Increased resistance (loose, corroded grounds) can cause this type of problem. Of course, you want to make sure you got the right alternator for your application. This other post may help:


Also, make sure to watch this other video:


Question: I have a 2007 Cadillac CTS. I replaced the battery, cranked up and the negative connection got hot. What would cause my Cadillac's battery to heat up?

Answer: If the negative cable gets too hot just cranking the engine, there's too much resistance in that part of the circuit. If this happened right after installing the new battery, probably the negative cable is not well connected or is damaged or there's some corrosion. You can also do a voltage drop test on that part of the circuit. These posts may help:



Question: I have an 03 Dakota. It needed a new battery, however, the battery gauge goes to 0, and the idiot light comes on after I drive it for a minute. It starts fine and the lights are fine; just that gauge quits working. What causes that?

Answer: Check the alternator, perhaps a bad voltage regulator.

Make sure the drive belt is not loose or the idler bad, causing the belt to slip. If the battery charge is not affected and everything else seems to work just fine, there could be a loose wire or connector in the circuit to the gauge.

Question: Bought a remanufactured alternator for my 2004 Civic today. I cannot get the wiring connector to snap back into the receptacle on the alternator. Can you give me some pointers, please?

Answer: Make sure the harness clip or connector is not damaged or broken. If the connector is OK, make sure you have the correct alternator for your particular model.

Question: When my engine is at idle the voltage is around 13V, but when I turn on the headlights and AC, it drops to 11V to 11.8V. What seems to be the problem?

Answer: My guess is the AC pulley may be putting a strain on the crankshaft pulley, affecting alternator output. Or the AC pulley is affecting the belt. Check how the three operate when the AC is on.

Question: On my 2003 GT Mustang, when accelerating, my battery light flashes 3 times. I've replaced the battery, my belts are tight, and my alternator voltage is reading 14.60 v the first time I checked, and second time it was 13.90 v. Can’t figure out what it is?

Answer: Check the connections. This other post may help:


Question: I've got a 1982 Chevy K10 6.2L and I swapped the alternator. It's charging but it's charging slowly. It's running at 12.80 volts constantly. I'm out of ideas?

Answer: Check the connections. A loose, corroded or damaged wire or connection can cause this type of problems:


If the alternator was working fine in the other vehicle, have the battery tested if necessary.

Question: I have a Nissan Wingroad and I had to replace the battery before 18 months of use as it wouldn't start without jump starting. When the measures were taken, the charging system measures were 13.560 volts on no load and loaded at 13.170. The battery vendor says that this indicates a charging system problem, but my mechanic says that there is no problem with those readings. The battery voltage was 14.09, cranking 10.590. What is the correct position, is there a charging problem or not?

Answer: Check the system specifications in your vehicle repair manual. If you don’t have the manual, your local public library may have a copy in the reference section. It’ll be more curate and you’ll avoid guessing. You can even do these measurements yourself with the manual. I don’t have the manual for the model.

Question: Why does my '99 Bonneville’s charging system go down to 12 volts only when in drive or while idling?

Answer: Usually, the voltage goes down under load and as the engine warms up. But you might want to check the alternator, battery and charging circuit if it dips below battery voltage. Having the charging system amperage may give you a better diagnostic of the charging system, if necessary.

Question: Can the dash charging gauge on a '67 Pontiac Catalina cause the charging system not to work?

Answer: It might cause problems with the regulator, but I don't have the schematics with me. If there are charging system issues, also check that the wire and connections going to the starter are all good.

Question: I have a 1990 Ford F-150 and the alternator stays hot and won’t charge the battery, any suggestions on what is wrong?

Answer: First, make sure the belt is properly installed, not slipping, and accessory pulleys are running OK. Check the charging system wires for loose or corroded connections or damaged wires. This other post may help here:


If necessary, have the alternator checked (worn, bad voltage regulator) and battery. Hope this helps.

Question: I have a Toyota Yaris sedan 2014 connected with an OBD 2 using torque pro to monitor. the other day, I suddenly lost power steering, the dash light came on, followed by the ABS light and the handbrake. After a while, the warning lights went off by its self, power steering was restored. It happened again yesterday. Could this be an alternator issue? My battery is new and 1 week old.

Answer: Check the serpentine belt and the pulleys it runs on. Make sure the belt is not damaged and the pulleys are working as they should. Check the pulleys for alignment as well. It seems the serpentine belt suddenly stopped spinning.

Question: I have a 2001 Toyota Solar, and the alternator keeps wearing out. Four out in a year in four years. It is a Toyota alternator, not an aftermarket. I have a new Interstate battery. Two repair shops looked and didn’t know why. Do you have any idea what’s going on?

Answer: Have your battery tested and also make sure all battery cables and their respective connections between the alternator and starter are tight and clean.

If there's too much resistance in the circuit, it'll wear out your alternator. Also, test the starter and charging circuits, if necessary.

Did they tell you how the alternator failed exactly? That can give you an idea about the issue as well. What about trouble codes? Scan the computer, just in case there are any pending codes.

Question: I have a new but cheap alternator. What could be causing such a large fluctuation in voltage?

Answer: The diodes could be leaking or shorted. Have the alternator checked before replacing it.

Question: I have a 2006 Ford Freestyle. Last year, the car didn’t want to start, so I replaced the battery. Five miles down the road, the battery light came on. I took it to the Ford Dealership to check the problem. They replaced the Alternator. A year later, I noticed the lights started to dim, then to fade back up. I took it to an Interstate battery shop to have the battery checked out. The battery was excellent, but the alternator showed low charge. What should I have the mechanics do next?

Answer: Although there is a remote possibility the alternator is failing, this may be a charging circuit (positive side) problem. If you explain to the shop when you replaced the alternator and about the battery and alternator test results, most likely, they’ll take a look into the charging circuit.

Question: 2002 Mitsubishi Magna. Battery 12.43v, drops to 11.98v at idle. 11.95v from alternator. There seems to be no AC leakage. Fuses all good. Wiring seems all good. Voltage to alternator from battery is correct (connector tested). Is the alternator just producing low voltage because the alternator is faulty? I should mention it is absolutely covered in oil from an oil leak; wiring is dirty but working. Could oil inside the alternator be the cause?

Answer: Oil can definitely affect the alternator. If you have fixed the oil leak, check the alternator circuit voltage drop to make sure it is not interfering with current. This other post may help:


Question: I have a 2000 Civic EX 2 door coupe. The alternator went bad, and I replaced it along with the battery. The car runs fine. It seems to charge the battery, but then the battery light comes on. I have driven the car, and I haven't had any problems running the AC, lights or radio. I can unplug the alternator, plug it back, and the light will go out. But as soon as I plug it in, the light comes on again. Doesn't seem to change the engine running or idle when I unplug the alternator. What could be the problem?

Answer: If there are any DTCs, clear them from the computer memory. Also, check the fusible links. Make sure they are still well connected and good.

Question: I have a ‘03 Chevy Silverado alternator that whines and displays a check engine code, mainly knock sensor. Occasionally cylinder 7 and 8 are too lean. I suspect a bad ground. Do you know where I can find a visual of where all the grounds are on this truck?

Answer: If you don’t have the repair manual for your specific model, check your local public library. They may have the manual in the reference section. Alternator whining sounds may come bad bearings, bushing or misaligned, worn belt, even a bad diode on some models.

Question: Will there be any signs in a Chrysler car battery terminal, if you remove the terminal that there is a problem with the alternator and charging system?

Answer: If the alternator is overcharging, there could be signs of corrosion; but the terminal may be cracked or loose. But you may find problems while the engine is running, but don't remove any connections while the engine is running. It can affect sensitive electronics. If you are trying to find a fault in the charging circuit connections, it's better to do a voltage drop test. This will tell you the condition of the connections. These other two posts may help you locate this type of issues with the charging system and engine grounds:



Question: I have a 2003 VW beetle. I have changed the alternator more than 8 times. I finally got the right one through the VW parts, but it’s still not charging back my battery, and I bought the battery a year and a half ago. I have been charging it and it still holding battery, so it’s driving me crazy as to why is not working. Can you help?

Answer: The problem could be in the circuit. If your particular model has a fuse (check your repair manual) it may be blown. Less likely, but it could happen, a fault in the computer can prevent the alternator from charging the battery.

Question: I have a 2207 Honda Accord, I replaced the alternator and cranked it It seemed fine. It sat and idled fine, but when I go to press on the gas the amps start dropping and the car will cut off. What could be making my car shut off?

Answer: Sometimes the problem is with the drive belt. Either the belt is loose or the belt tensioner is not working properly. The belt might be slipping when rpm goes up. Check the belt for wear. Most belts are changed at around the 100,000 miles, or sooner depending on mileage. Check the slack. If you need to change the belt, replace the tensioner as well.

If necessary, check the wiring to the alternator and electrical connector for loose, corroded or damaged wires. And have the battery checked.

Also, check the charging voltage across the battery terminals with a digital multimeter. Make sure the gauge is working properly.

Question: I use a Golf 4 alternator on a Golf 4 as I saw fit. It runs fine, and there aren't any alarming sound. The problem is that it doesn't charge when I start the car. I have to rev the engine hard, and then it starts to charge normally. What the problem?

Answer: If the warning light is coming on when you rev the engine, check the light circuit. specifically, you should check the resistors in the gauge cluster.

Check the drive belt first for tension and wear. Also, make sure that the back wires are properly connected and clean. Then, check the voltage regulator.

Question: What would cause a new alternator to whine and have the pulley heat up excessively? Starting at ambient air and shooting up to 275+ degrees. But when the battery cables are disconnected while the engine is running, the alternator pulley runs smooth and there is no excessive heat build up. The battery is also brand new.

Answer: This is usually caused by a faulty diode(s), making alternator work extra-hard. Check voltage output; also, check the charge circuit voltage drop:


Question: I have a 2004 Chevy truck and the gauge will stay at 14 volts but sometimes it’ll drop down to 12 volts. Is this normal?

Answer: Check for a loose connection, wire or cable between the battery and the alternator. Wiggle the wires and see if the voltage changes. Also have the alternator checked, if necessary.

© 2017 Dan Ferrell


Dan Ferrell (author) on August 31, 2020:

Make sure the alternator is properly wired. You may need the manual for your particular model. Assuming you got the correct alternator and battery for your application, check how much drain your engine and accessories are putting on the charging system. Aftermarket components (sound system) can tax the charging system. Also, you may want to check for proper connections. Troubleshoot for unusual voltage drop. This other post may help:


Hope this helps.

glanton on August 30, 2020:

o have a 2000 chevy silverado 4.3 i put new alternator and battery and relays but yet its still dragging where dose the one wire go to from the alternator and why dose it keep dragging

Dan Ferrell (author) on August 19, 2020:

Have the battery checked to see if there was any damage. And check the circuit fuse for the radio. It's probably blown. Most auto parts stores will check the car battery and alternator for free. Consult your car owner's manual or vehicle repair manual to locate the fuse, if necessary. Hope this helps.

Joeyjandreau@gmail.com on August 18, 2020:

My altimetre was over charging my battery Shall I changed the alternator and a battery with a new one and ever since that my radio don't work what could be the problem

Dan Ferrell (author) on August 12, 2020:

Maybe there's an issue with the circuit or you may be expecting a charge at a low RPM threshold. Hope this other article may help a bit:


Tommy clark on August 12, 2020:

I have a self exciting alt, 24v it only stays excitied when i have the warning lamp hooked up. But when removed alt dose not stay excitied

Dan Ferrell (author) on July 22, 2020:

Here are some thoughts. It's possible the vehicle's diagnostic system is causing the light to come on after replacing the battery and/or alternator. Did you have your reconditioned alternator tested to make sure it was working properly?

The problem may also come from a faulty connection, wire or cable. Don't forget any relays or fuses in the circuit. Make sure all the connections to the alternator are tight and clean. Visually inspecting circuit connections may not reveal any problems, but checking the circuit for voltage drop may tell you the condition of the connections themselves and the wires/cables (check for corrosion, loose or damaged cables). This other post can help you check circuit voltage drop:


Hope this helps.

Reihana Ria on July 22, 2020:

I have a 2000 peugot 206 Alternator recondition, new battery when driving battery light comes onys on

Dan Ferrell (author) on July 20, 2020:

Make sure the alternator connectors and wires are tight and good, specially if the previous alternator was working find. This other post may help:


maggie on July 18, 2020:

So I recently replaced my alternator and when I start the car my voltmeter reads the charge on the battery goes from 12.6 to 6.58 volts. I am not sure what this means I'm assuming an under charge but I'm not sure

Dan Ferrell (author) on July 10, 2020:

There might be a surge in voltage if the connector is loose and voltage is trying to make it pass the unexpected resistance. You may want to have the alternator tested. Also, check the voltage drop in the charging circuit. This other post may help:


Hope this helps.

Big bad wolfman on July 10, 2020:

I have a new battery and just put a new reman alternator in and checked the voltage and I was getting 13.5-14.0. Volts so it was working good. Turned it off 30 minutes later I got in it to go somewhere and it was still charging good, didn’t get 5 miles down the road and the battery light came back on and it’s not charging again. Can it kill the alternator if the connector comes out while the engine is running? I know on a Harley it damages the voltage regulator if it comes unplugged while it’s running but if you unplug it before you start it it doesn’t hurt to run it other than the battery will go dead. It’s in a 2008 Chrysler 300c 5.7

hardlymoving from Memphis, TN on June 22, 2020:

Easiest way to check for alternator problems is to install an accessory port / cigarette lighter plug LED digital voltage display. As you drive the car, you can monitor the voltage to see if the alternator is putting out over 13v at all rpm's. If less than 13 and dropping, replace the alternator ... unless it's a Honda with a defective ELD (electronic load detector).

Dan Ferrell (author) on June 19, 2020:

If your battery and alternator test good, check the charging circuit. This may help:


Paul Rittenberry on June 19, 2020:

My car is discharging

Dan Ferrell (author) on June 12, 2020:

The fusible link is there to prevent damage from a surge in current. Install a fusible link or the cable for your application. If you're still having charging problems, you might want to check the circuit. This other post may help:


Blu on June 12, 2020:

I been jumping my battery off every time I go somewhere for over a week i thought it was my battery but it was my alternator i put a new one on and it's not holding at 14 or more when its running i also turned on my lights and more i got rid of my other battery cable it had a fusible link and I put on one that didn't would that make a

Dan Ferrell (author) on June 10, 2020:

Have the battery checked. If it's good, check the charging system circuit tested. Checking the circuit voltage drop will help. This other post may help:


April fishel on June 10, 2020:

I have a 1999 jeep cheakee and the alteenate has been tasted and is good but. My truck still will start but will shut off once batterie is dead. It is not charging and i cant figure out why if ault is good.

Dan Ferrell (author) on May 14, 2020:

Start with the parasitic drain issue. This other post may help:


You may need the diagram for your particular model charging system to locate the short. You buy a relatively cheap aftermarket manual in most auto parts stores. Hope this helps.

David on May 13, 2020:

My Chrysler 300c 2005 won't charge battery I bought New alternator and New tipm same problem no charge I have a fuse that keeps blowing up when I put the alternator diode fuse on and my sun roof don't work my radio and air conditioning and heater won't work I don't know if it is a ground because it has a parasitic drain please help I'm spending money mecanik are taking my money and car is the same

Dan Ferrell (author) on May 04, 2020:

Make sure the battery is in good condition. Then, check the voltage drop on the charging circuit:


Then, have the alternator checked, if necessary.

Gima on May 04, 2020:

I have a problem with the alternator for COLORADA DMAX, I cannot seem to start the vehicle, we only start the vehicle once we charge the battery.Hoever this does not last, we can only start the veichle once the battery is charged.Please help?

Dan Ferrell (author) on February 25, 2020:

Have the battery tested at your local auto parts store. If the battery is good, then check the charging circuit. This other post may help:


Susan on February 25, 2020:

I hv a honda crv alternator is good condition but battery is not charging

Dan Ferrell (author) on February 10, 2020:

There could be a problem with the voltage regulator. Also, you may want to check the charging circuit. This other post may help:


Martin on February 08, 2020:

New battry fitted yesterday new alternator last year when put new battry on it is now charging at 16.45 volts any ideas could it be a faulty battry cell .

Dan Ferrell (author) on January 27, 2020:

There could be a problem in the charging circuit or engine grounds. Also have the battery and alternator checked, if necessary. These other posts may help:



Lori amdahl on January 27, 2020:

I have a GMC truck my daughter left two of the interior lights on when she got out eventually I think they automatically shut off when I went to start it that morning Deb interior lights come on to show they were left on it started right up I only live maybe four blocks from work went to work shut it off came home at lunch went back then she took it to work a lot farther a couple miles or so down the road she got gas shut it off when she went to start it it kind of did the click click click the click a friend charge the battery the keep has been popping off but when she drove it it was like start acting like it wanted to die and the lights went down but I don't know I get I wasn't with her so I'm not sure would that be that battery or could that be the alternator

Dan Ferrell (author) on December 28, 2019:

Make sure you got a good battery, Have it checked if necessary. Also, check the charging circuit for a bad connection. This other post may help:


Check engine grounds:


Jay on December 27, 2019:

Hi i have a 2000 ford E350 super duty i put 3 used alternators on and they were bad i got oringinal rebuilt and put it back on van but still not chararing my battery lights does not cum on at all i took to auto supplie to take it and the always say voltage regular bad could my van be making it go bad everytime i put it on there im just lost i dont what to do i just the van n was told all it needed was an alternator im pulzzed

Dan Ferrell (author) on December 24, 2019:

Have the battery checked first. Then test the alternator. Often, engine grounds or loose wires or connections in the circuit can cause this problem. These other posts may help:



Lu on December 23, 2019:

Have 06 scion tc replaced alternator with a 05 that was in junkyard said they tesed it but battier still does not charge. Light dim and radio and everything turns off as battery drains is that my alternatoe

Dan Ferrell (author) on December 19, 2019:

it's possible the alternator is overcharging or the battery is faulty. Do the test #5 in section II. That'll help you diagnose the problem, if there's one. Hope it helps.

Victor on December 19, 2019:

I have a corolla 93 model

When i start my engine at idle rpm @1k

The voltmeter reads 15v is it normal..

I just replace my ecu because its faulty.

Jim on October 26, 2019:

Hello there Dan!

Dan Ferrell (author) on October 21, 2019:

A bad fussible link between the starter solenoid and alternator sometimes cause this problem. Check all the fuses and check for trouble codes. If you don't have a scanner get a free scan from your local auto parts store. Sometimes a sensor may cause this problem as well.

Lisa Williams on October 21, 2019:

I have an 07 Hyundai Sonata I’ve had the alternator replace an the servertine belt my battery light an brake light an air bag light is on plus my ac don’t work it was working all before

Dan Ferrell (author) on October 08, 2019:

Check the charging circuit voltage drop. There may be too much resistance, causing the alternator's temperature to rise:


Hope this helps.

Thomas messner on October 08, 2019:

My battery goes dead after 2days , I have noticed that my dash charge cluster goes up & down only wen I use signal or wipers is there a bad cluster or wiring, I hav changed alternator 2 times it gets hot to touch wat is problem?

Dan Ferrell (author) on October 03, 2019:

it seems the probelm is either in the charging circuit or the engine grounds. Check the wires for the alternator and the circuit. These other two posts may help:



Chris Ramirez98 on October 03, 2019:

hello,I have a 99 Lexus ES300 and I've been having major electrical problems with her. started to show the first symptom of not starting (would need a jump about once a week or two) next the car would struggle to start, then the lights in the cab and headlights were going dim, next they were vigorously pulsing and get faster with the speed of the car. we have replaced the battery, alternator, starter, positive cable leading to starter (it was visually very corroded) and made sure all connections were secure. the car starts to loose power after driving and we have concluded so far that the car is running off the battery solely Another symptom is the dash lights and center console loose power first as a warning the the car is about to die. the RPM needle goes wacky and then the car is struggling to move forward. if you cut the lights and radio and A/C in this situation the car gets the last amount of juice and rides good again enough to get to a safe place. We don't know what it is and have begun looking at the grounding cables and still flying blind trying to solve the issue. help is very much needed to anyone who has expertise. please help me. (after replacing the alternator the battery light has been consistently on even with the change of the other parts.

Dan Ferrell (author) on September 17, 2019:

There could be a problem in the charging system. If the computer regulates voltage output in the system, check there too. Try checking for trouble codes, even if the check engine light is not on. There could be a pending code.

Claburn on September 17, 2019:

Hi Dan got a 2017 pathfinder battery light cane on car stop moving . Had celeration in Park and neutral but not in drive change the alternator all was fine for a week and the sane problem again any answers .

Dan Ferrell (author) on September 09, 2019:

There could be a loose wire in the circuit. If you need to test the alternator, this other post may help you:


Stone Emmanuel on September 09, 2019:

Please i have a 2003 golf 4 when ever i start the engine will start normally, i expect the Alternator and the fan to start working but i notice i have to raise my car before the Alternator will start working even when the engine is hot ...i just have to raise the car b4 the alternator will start working...what can i do

Dan Ferrell (author) on September 07, 2019:

Probably the nut holding the stud to the rectifier is loose. You can try taking it apart and tighten the bolt. If the insulator is damaged, you'll probably need to replace the alternator, unless you can install a new battery stud kit.

Zerina Wilson on September 06, 2019:

I cannot get the bolt to connect battery to alternator tight. Is there a way to tighten it do I take alternator apart and replace the Standard Ignition Alternator Terminal?

Dan Ferrell (author) on August 27, 2019:

Check the fuses and the electrical connectors. A wire might come loose or a fuse blown when they replaced the alternator. Hope this helps.

Jannin on August 26, 2019:

I had my alternator changed but now my lights will not come on nor will my alarm work what can be done to fix it?

Vaderdude on August 06, 2019:

Nice job here.

I would love other people's two cents on these. For the sake of argument, presuming there is no parallel causes.

1- Is it possible to cause a short if the battery is hooked up back with the alternator removed? In this case presume that all connectors are protected and not exposed, not dirty, rusty, oxidized, compromised, etc ....and in excellent conditions.

2- Spraying electrical connectors with proper electronic cleaner, could it potentially cause troubles, assuming that connector were not damaged by handling....

3- Can oil spill on connector potentially cause a short?

Thank you for sharing your opinion and experience.

Dawit Berhe on June 10, 2019:

Keep it up

Dan Ferrell (author) on May 24, 2019:

Check the charging system circuit. Sometimes the fusible link, if the circuit has one, is the faulty part.

Dan Ferrell (author) on May 24, 2019:

Check the charging circuit. If it is Okay, the circuit to the warning light is shorted.

Malcolm Jenkins on May 24, 2019:

Both my battery and alternator are good but i still need jumps

Vijanda on May 24, 2019:

Hi my alternator was repaired but if i pulled out one battery plug the car go off but the battery light is off.

Dan Ferrell (author) on May 02, 2019:

There's a special circuit for the battery indicator on the dashboard. Something is feeding power to the circuit, possibly a bad ground. You might want to ake a look at the wiring diagram at the repair manual for your model. If you don't have the manual, check the reference section of your local library. Hope this helps.

Justin on May 01, 2019:

My 97 4Runner has had a battery light on for 2 years now. Hasn’t effected driveability. Installed a voltemeter to read battery output and is always 12.4-12.6 off and 13.6-14.1 on. Question is what would be the cause of my light if there’s not an over charge or under charge? Like I said been on 2 years along with abs light. What’s the cultiprit

Dan Ferrell (author) on April 17, 2019:

This usually occurs when the ignition coil develops a short that causes high current draw, overheating the module and eventually burning it. Look for white residue under the cap (if module is located inside). You might want to check the coil or have it checked. This post may help:


When replacing the module, make sure to apply the grease to the backing plate of the module, and if possible, use only the OEM product. Hope this helps.

Adam on April 17, 2019:

My dad's Honda ballad 150 1995 keep on burning the modules one after the other it doesn't even start

Dan Ferrell (author) on March 21, 2019:

It is wearing out the belt and putting a stress on other pulleys and engine. If you plan in fixing the AC at a later time but want to use the car, you can try finding a shorter serpentine belt or install an AC compressor bypass pulley. Just search online for your specific model. Hope this helps.

Orlando on March 21, 2019:

Having trouble finding exact issue on my 05 ford escape. Trying to avoid spending too much for a part that wasnt the problem. A question, if a/c compressor pulley is not free spinning on its own but belt is sliding right past it as intended would that put strain on any other parts associated, with desired effect. Like other pulleys or not maintaining a charge on battery?

Dan Ferrell (author) on March 15, 2019:

Check this other post:


jason.jjcm@gmail.com on March 14, 2019:

1995 Honda Accord engine won't start

Dan Ferrell (author) on February 16, 2019:

Most likely there’s a problem in the charging circuit, since you have a charging problem. If you have the wiring diagram for the charging circuit (vehicle repair manual), locate the wire for the warning light. Usually this is marked IND or WL on the back of your alternator, but double check your diagram. Ground this wire and turn the ignition to On. If the warning light comes on, there’s a problem in the circuit; otherwise, the bulb is blown. But I believe, even if the bulb doesn’t come on, there is a problem in this part of the circuit causing you trouble. Hope this helps.

Bolara from USA on February 15, 2019:

Hello . I have a 2009 Toyota Avalon XLS

One day all lights flashed and shortly they went off and the car stopped. I was told it’s the alternator and it was replaced and problem was fixed , that was a year ago . Yesterday I had the same problem and Firestone said it’s the alternator. The problem started a week ago when battery light flashed for a minute then disappear and come back days later and disappeared until yesterday when the car stopped. I have doubts about the alternator as the battery light is not on before engine start or after . It’s simply not there yet the alternator is not charging . I disconnected the alternator cables and started the engine to see if the light will come on with the alternator disconnected, but no , it didn’t come on at all . Now I am confused. I don’t want to pay another $ 600 to replace the alternator. I need to understand why the alight is not on when the alternator is not charging? What to do . Everything around the alternator looks clean and functional. Any help ? Thank you

Dan Ferrell (author) on January 28, 2019:

You might want to try checking the circuit voltage drop, there could be a bad wire you can’t easily see just by looking at it. This post can give you an idea about checking for voltage drop:


Malik on January 27, 2019:

Question. I have a 2000 lexus gs300 the alternator is reading bad voltage regulator. Ive changed the alternator 3 times. when i get them bench tested they pass but when i put it in the car it fails. Ive checked my wires, cleaned my ground connectors, and checked the fuses. PLEASE HELP?

Dan Ferrell (author) on January 23, 2019:

You may want to do a voltage drop test on the charging circuit (between battery positive and battery connection on the alternator; and battery negative and alternator ground).

This post gives you an idea about the test:


Adrew Jackson on January 23, 2019:

I have a 1999 ford f150 and after i replaced the battery the truck was still losing power. So i replaced the alternator. Now im losing power but nowhere near as fast, but its still happening.. what could the problem be

Dan Ferrell (author) on January 19, 2019:

Have the alternator checked. There could be a problem with the voltage regulator.

Steve Swaddling on January 19, 2019:

How do I find a short for an overcharging alternator

Dan Ferrell (author) on December 13, 2018:

You need the wiring diagram for your particular make and model. Check where those wires connect to and see if yours is supposed to have a reading.

Timothy Mason on December 13, 2018:

I have a 2012 kia sorento. pulled the alternator had it check on a bench test and it passed. The power wire, fuseable links, fuses all with alternator still out of the car. everything came back with the normal .2 .3 ohms reading. I found an aritcle that said to connect the black wire of my multimeter to the ground on the batter and positive check the 4 insertes of the plug that connects into the alternator. The video showed all 4 had a reading mine only showed one. So i did the opposit placed the positive on the batter and negavitve checked my plug and the opposite one gave a reading but again not all 4. Is it supposed to have a reading in all 4 plug ends? And if not what else can i do to diagnose where my short is?

Dan Ferrell (author) on November 22, 2018:

There could be a problem in the charging system. The noise may come from a pulley, making the belt loose. This other post might help:


Loveis on November 22, 2018:

Hi, Thank you in advance! I have a 2001 Infiniti g20 and It starts but wont stay running and the battery is draining after I charged it at autozone. I just replaced the alternator and still wont stay running. I do hear a loose pulley or something near the alternator, but don't know exactly where yet. What else can I do to get the car running again. It will run, just battery died quickly and abs and battery light flashes on and off. Can you give me any pointers? Thank you!

Dan Ferrell (author) on November 14, 2018:

It's possible you have a loose wire or connection. Have somebody watch the warning light while wiggling wires and connections and see if the light comes on. Also, you may want to try doing a voltage drop on the charging circuit. This post will give you an idea about how to go about it,


Noah Smith on November 14, 2018:

I just replaced my alternator on my 06 mustang gt. The diodes were bad and was causing a check engine light ive never had the battery light come on. But it came on right after i changed the alternator. It comes on for a few seconds then turns off for a while. Ive already double checked my work. And tested the battery with the car running and the battery stays around 13.7 volts.

I dont want to drive my car until i figure it out. I Dont want to get stranded.

Dan Ferrell (author) on October 11, 2018:

Sorry, I'm not familiar with the system, but probably this might help you. Good luck


Dan Ferrell (author) on October 11, 2018:

Hi Mayo,

Go over section IV in the post. This might help with the problem.

Good luck.

LB Mayo on October 11, 2018:

1993 F250 4x4 7.5 gas engine. I am having charging problems any time I run ac or headlights. New alternator, new alt. Belt, cleaned batt.post,cables and all wires on fender mounted starter solenoid. Had battery checked twice. What else could it be?

RJ SAYMO on October 11, 2018:




Dan Ferrell (author) on October 10, 2018:

Hi John,

It seems as if there's something drawing too much power. Possibly an amp? But why the headlight go dim with radio off, but with headlamp and AC on (and radio still off?) the charge maintains. I'd start by checking the alternator and battery fist. Make sure they are good.

John on October 09, 2018:

I have a Hyundai i10 year 2010, my car have a 13.3V charge (idle) when I switch on headlamp and AC at the same times, radio will on and off for 1-2 seconds (idle), headlight will go dim when radio is off. When RPM2000, charge will increase to 13.6V.

If I only switch on headlamp / AC, charge will maintain 13.8-14.2V.

Is it my car's alternator problem?

Dan Ferrell (author) on October 01, 2018:

remove the belt and try spinning the AC pulley by hand. It should spin freely - if there's noise or the pulley feels rough,noisy, you'll need to replace it.

Douglas Anayabere on September 30, 2018:

My compressor belt is dragging when i switch the aircondition on. What is the problem?

Dan Ferrell (author) on September 21, 2018:

Hi Ron,

Check the voltage regulator.

Hope this helps.

Ron on September 20, 2018:

Put new battery and altinator on 2001 f150 and its still over chargeing is it the pcm?

Dan Ferrell (author) on September 08, 2018:

Hi Aaron

Check the battery cables for corrosion and make sure they are tight. Also check the connecitons to the alternator and wires. Also, make sure the alternator belt is not loose or worn. If all that turns out okay, check the battery. An auto parts store will check the battery for you, if necessary.

Hope this helps

Aaron on September 08, 2018:

My corolla 2e battery light remain even when the alternator is charging. What could be the fault?

Dan Ferrell (author) on August 13, 2018:

Hi Keith,

I don't have the diagram with me but probably this pic might help. I believe is the same model.


Otherwise you can check the repair manual in your local library.

Good luck

Keith Irons on August 12, 2018:

Need to know what does the spade connecter go to for 1982 bmw 320i on the alternater

Dan Ferrell (author) on August 10, 2018:

Hi Enos,

They should test the circuit (wires and connections), ground (engine) connections and make sure the correct output voltage is coming out of the alternator and getting to the battery.

Good luck

Enos Kaufman on August 09, 2018:

alternator was changed even the one changed out tested fine Napa still flatlined im lost now

Dan Ferrell (author) on August 07, 2018:

You might get occasionally over 16V from the alternator. Have your battery checked at a local auto parts store.

Don on August 07, 2018:

How about of light is on, but have 24.3 volts at the battery while running, 14.4 volts at the alternator, no dimming of lights or starting complications? 2018 ford F-59

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