Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.
Ten Reasons Your Car Won't Start
1. Dead battery
2. Bad starter motor or system
3. Faulty alternator
4. Clogged fuel filter
5. Faulty fuel pressure regulator
6. Bad fuel pump
7. Faulty ignition coil or module
8. Faulty crankshaft position sensor or camshaft position sensor
9. Major vacuum leak
10. Failed timing belt
Later in this article, we'll help you navigate through some tests to decide which problem is yours so you can get back on the road.
Five General Categories
Your problem very often fits into one of these five categories:
- Discharged battery
- Faulty starter or alternator
- Fuel system issues
- Ignition system problems
- Bad sensor
A Few Recommendations Before You Start Your Diagnostics
- Don't skip the obvious. For example, make sure you actually have gas in the fuel tank, and that your battery is charged and has clean and tight connections.
- Start by going over the first two sections below. They can help you zero in on the potential problem and check for fuel delivery issues, if necessary, to save you time and, possibly, money.
- Also, it's a good idea to have the repair manual for your particular vehicle make and model. You can buy a relatively inexpensive copy through Amazon. A Haynes manual can help you locate components. It also includes step-by-step procedures, systems descriptions, and images and photos for many maintenance, troubleshooting and replacement-parts tasks—so you can recoup your small investment soon.
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Pre-Diagnostic 1: Using Sound as a Diagnostic Tool
When dealing with an engine that refuses to start, you can use sounds, or the lack of them, as a diagnostic tool. Sounds help you focus on the system or systems where the problem could be located, eliminating other potential trouble spots.
What Sound Do You Hear When Trying to Start the Engine?
1. A single click
If you hear a single, solid click when attempting to start the car, the problem could be located in the starter motor or circuit.
2. A rattling sound
A rattling sound coming from under the hood when you try to start the engine may point to an undercharged battery, loose or corroded battery terminals, or a problem with the alternator or charging system.
3. No sound at all
If you don't hear anything when attempting to start your car, check for:
- A dead battery
- A loose ground (battery or engine)
- Loose or corroded battery terminals
- An electrical open in the ignition system
- A blown starter fuse or fuel pump
4. The sound of the engine turning over
When you turn the ignition key to fire up the engine, you may hear the usual roaring of the engine, but the engine never actually starts. If so:
- Make sure the fuel pump is being activated when you turn the ignition key to the "On" position–listen for a buzzing sound that lasts about 2 seconds. If there is no buzz, voltage is not reaching the pump, or the pump has failed. Check the circuit.
- Check for fuel delivery. See the next section.
- Check for a clogged fuel filter, if little or no fuel is reaching the cylinders.
- Make sure the ignition system is delivering a spark to the spark plugs.
If necessary, see the Resources section at the bottom of this post for help on these and other issues.
Pre-Diagnostic 2: A Quick Fuel System Delivery Check
Often, a no-start condition can be traced back to a fault in the fuel system. If your engine turns over but refuses to start, do this simple test. This test can tell you whether the problem is related to fuel delivery.
- Remove the air duct so that you have access to the throttle body.
- Spray some starting fluid past the throttle valve.
- Try starting the engine.
If the engine starts for a couple of seconds and then dies, your problem is most likely fuel-related. Check the fuel filter, fuel pressure regulator, and fuel pump, as indicated in the following sections.
The following video shows you how to use starting fluid.
Ten Common Faults and How to Check for Each One
Now that you have an idea of what system needs to be investigated, you can start investigating. The next ten sections deal with the ten most common faults you are likely to deal with when your car refuses to start, and how to go about checking for each potential fault.
1. The Battery Is Dead
This is one of the most common reasons a car won't start. A car battery may last up to six years, depending on maintenance and operating conditions. Extreme weather conditions, for example, will shorten its service life.
However, it's not uncommon for a battery to suddenly lose its charge.
Check the battery terminal connections. Remove corrosion and make sure the terminals are tight. Then check the electrolyte level if the battery has removable caps.
When your car refuses to start, make sure your battery has a good charge. You can use a digital multimeter (DMM) to check its state of charge.
To check the battery's state of charge:
- Turn all accessories off, shut the doors and pop the hood open.
- Set your voltmeter to 20V DC.
- Turn your DMM on and connect the black lead to the battery negative (-) post and the red lead to the battery positive (+) post.
- Your battery should have at least 12.4 Volts; otherwise, charge the battery or have it checked at your local auto parts store.
If you need to recharge the battery, use a slow charge, if possible. This will help restore battery condition.
Your local auto parts store can check whether your battery is still good.
2. Bad Starter Motor or System
The starter motor and its circuit are other common sources of trouble. This system could be the culprit if you hear a solid click when attempting to start the engine.
There could be a problem with the starter solenoid, relay or starter motor. If necessary, check the circuit with a voltage drop test. See the Resources section at the bottom of this post for help with this test.
Also, your local auto parts store will check the starter motor for free, but you'll need to remove the starter from the vehicle.
3. Faulty Alternator
Along with a dead or bad battery, alternator issues are one of the most common reasons for a no-start condition.
Usually, the charging system will turn on a warning light on the dashboard alerting you about a fault in the system. However, there are many reasons a charging system may fail to deliver a charge to the battery or electrical power to other systems in the vehicle.
Points to check:
- Check for a loose or worn belt or a worn or damaged belt tensioner.
- Inspect the condition of the wiring and connectors.
- Have the alternator checked at your local auto parts store.
- Do an alternator circuit voltage drop test, if necessary. See the Resources section.
Keep in mind that a corroded battery terminal could be a sign of an alternator overcharging the battery.
If you don't want to do it, your local auto parts store will check the alternator for you.
4. Fuel Filter Clogged
Most manufacturers recommend replacing the fuel filter every one or two years. Replace your fuel filter as recommended.
Although many fuel filters include a bypass valve in case the filter clogs, not all come equipped with this valve. Besides, rust and other sediments in the fuel tank can make their way to the fuel filter and clog its filter element.
Before giving out completely, a clogging fuel filter will give you one or more signs. For example, you may notice a lack of engine power at high speeds, difficulty starting the engine, or poor acceleration.
Check your repair manual to inspect the fuel filter and system in your particular model, if necessary.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the second section of this post.
5. Faulty Fuel Pressure Regulator
A fuel pressure regulator (FPR) limits the amount of pressure buildup in the system, typically to between 35 and 45 psi. Check your vehicle repair manual for your model specifications.
But FPRs can fail. If the internal diaphragm begins to leak fuel into the intake manifold, pressure will drop, and the cylinders will be flooded with fuel, making the engine hard to start.
Also, if too much raw fuel reaches the catalytic converter, the Check Engine Light (CEL) will begin to flash on your dashboard.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the "Pre-Diagnostic 2" section of this article above.
You can perform a few FPR tests at home. See the Resources section at the bottom of this article for some help.
6. Bad Fuel Pump
Fuel pumps have a long service life. They can last 80,000 miles or more. If your fuel filter and fuel pressure regulator are fine, but you have a fuel issue, probably your fuel pump is bad.
When turning the ignition key to the "On" position, before trying to start the engine, you should hear a buzzing sound for a couple of seconds. This is the sound of the fuel pump motor being activated to prime the fuel delivery system.
If you don't hear this sound, it may be that:
- No voltage is reaching the fuel pump
- The fuel pump fuse is blown
- The fuel pump relay is bad
- The pump itself may have failed
To verify a fuel delivery issue, do the quick fuel system delivery check as described in the second diagnostic section near the top of this article.
Also, check the repair manual for your particular model to see how to test the fuel pump, if necessary.
7. Faulty Ignition Coil or Module
For the most part, ignition coils or modules are pretty reliable. Unlike spark plugs, wires, and distributor caps (depending on the model), an ignition coil or module doesn't require much attention.
However, they can fail from time to time. The conditions under which they operate, like heat, vibration and other engine performance issues, can have an adverse effect on any of these components after many miles of operation.
Older vehicle models used a single ignition coil and module to deliver a spark to the spark plugs. Newer models may use a module and one coil per spark plug. A failed coil or module in one of these models will certainly prevent the engine from starting.
You can use a spark tester to verify the presence and condition of the spark. You can buy one at your local auto parts store. If possible, get an adjustable spark tester you can use in different vehicles.
The Resources section at the bottom of this post, and your vehicle repair manual, can help you check an ignition coil or test for the presence of a spark in the ignition system.
8. Faulty Crankshaft or Camshaft Position Sensor
The crankshaft position (CKP) sensor monitors engine speed, and the camshaft position (CMP) sensor tracks the position of the camshaft.
The electronic control module (ECM), the car's computer, uses the signal from both sensors to control fuel injection operation, direct ignition, and, depending on the vehicle model, the variable valve timing system.
If any of these sensors fails, your car may fail to start.
Sometimes, depending on the specific fault, a bad CKP or CMP will trigger the check engine light (CEL). Whether the CEL illuminates on your dashboard or not, it's a good idea to scan the computer memory for potential diagnostic trouble codes (DTCs) that can help you diagnose a no-start condition.
If you don't have a scan tool, your local auto parts store may download DTCs for you without cost.
Also, check your vehicle repair manual. And, within the Resources section at the bottom of this post, you'll find links to other posts to help you check these sensors yourself, if possible.
9. Major Vacuum Leak
Major vacuum leaks are not common, but they definitely happen. A vacuum leak can make the air-fuel mixture too lean, preventing the engine from starting.
A leak may come from a vacuum line, intake manifold gasket, throttle body gasket, leaking EGR valve gasket, power brake booster or positive crankcase ventilation (PCV) valve.
Vacuum leaks can be tricky to find. You can visually inspect every vacuum hose and trace it with your hand, feeling for tears or damaged spots. Also, pay attention to hissing sounds that may indicate a leak.
A leaking gasket is harder to detect, though, unless you have a smoke machine designed for this purpose.
If necessary, consult your vehicle repair manual.
10. Failed Timing Belt
You won't see this type of failure often. Timing belts can last between 50,000 and 100,000 miles or more, depending on your particular model. And if you have a timing chain rather than a belt, you may never have to worry about replacing it.
Still, if you've checked the usual suspect without success, check for a failed timing belt or chain.
The engine's crankshaft and camshaft are joined by a timing belt or chain through a series of sprockets. When this belt or chain brakes or wears out, or the tensioner fails, the crankshaft won't be able to rotate the camshaft anymore, making it impossible to start the engine.
Checking for a failed timing belt or chain:
On a vehicle fitted with a distributor, you can remove the distributor cap and try to fire up the engine. If the distributor rotor doesn't move, most likely your timing belt or chain, or one of the system components, has failed.
On models with multiport fuel injection systems, sometimes it's possible to remove the timing belt or chain cover to check for camshaft movement while trying to start the engine. Or you may be able to remove the oil cap from the valve cover, or the cover itself if necessary, to check for valve movement while trying to start the engine. If there's no movement, it's time to check the belt, chain, or system components.
If the camshaft rotates, you may still want to verify ignition timing. If the belt or chain has skipped some sprocket teeth, it may be difficult or impossible to start your engine.
Consult your vehicle repair manual to check crankshaft and camshaft synchronization.
A Few Unusual Additional Possibilities
Of course, there are other model-specific components or systems that can prevent your vehicle from starting. For example:
- A faulty key fob or with a drained battery.
- Inertia fuel shut-off switch triggered during an accident or a jolt on the road.
- Faulty anti-theft system.
Consult the repair manual for your specific make and model for help on these and other systems or components.
Dealing With a Car That Won't Start
To sum up, when your car won't start, begin your diagnostic with the most simple components or obvious potential problems, as in Diagnostics 1 and 2 at the beginning of the article:
- Make sure there's gas in the fuel tank.
- Verify your battery's state of charge.
- Make sure battery terminals are clean and tight.
- Check the battery and engine ground connections.
- Verify the fuel pump is energizing when turning the ignition key to On.
- Check for blown fuses.
Then you can start checking the alternator, starter motor, ignition, fuel system pressure, and their circuits.
Most of the time you'll be able to fix the problem yourself. Sometimes, you will need to replace a fuel pressure regulator, ignition coil, module, or fuel pump, or fix a vacuum leak.
See the Resources below for diagnostic ideas if you have narrowed your problem down to a particular system.
Resources on Starting System Faults
- Car Starter Problems? Five Starting-System Inspection Tips
Car starter problems? Don't blame the starter motor yet. These 5 troubleshooting tips will help you find the culprit.
- How to Use Voltage Drop to Troubleshoot the Starter System
Testing the voltage drop can help you find trouble spots in your starter circuit before you swap components unnecessarily.
Resources on Charging Circuit Faults
- Troubleshooting Alternator and Charging System Problems
Diagnose alternator and charging system problems with this practical guide to get your car back on the road faster.
- How to Do a Voltage Drop Test on Your Charging System
Voltage-drop test your charging system circuit before condemning your alternator.
Resources on the Fuel System
- How to Test a Fuel Pressure Regulator
Learn how to test a fuel pressure regulator to save money and time in car repairs.
Resources for Dealing with the Crankshaft and Camshaft Sensors
- How to Test a Crankshaft Position Sensor Using a Multimeter
Troubleshoot an inductive or Hall effect type crankshaft position (CKP) sensor using a digital multimeter.
- Camshaft Position Sensor Test
You can do a camshaft position sensor test using a digital multimeter at home and, if necessary, using a few common tools.
- My Engine Has No Spark at the Coil
If your car’s ignition system has no spark, a few simple tests can help you locate the fault.
Resources for Dealing With Battery Faults
- How to Test a Car Battery With a Multimeter or Hydrometer
This guide will show you how to use a digital multimeter, hydrometer, and other simple tools to troubleshoot, inspect, and clean your battery if necessary.
- How to Do a Parasitic Battery Drain Test
Find that parasitic battery drain that's causing your car battery problems whether you have a newer or older vehicle model.
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.
© 2021 Dan Ferrell