Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.
An electrical circuit needs a good ground to function correctly. A bad electrical ground may affect one or more electrical systems because it forces current to search for other easy paths back to battery ground. This may cause all kinds of trouble for lights, sensors, modules and other electrical and electronic components.
Causes and Symptoms of Bad Engine Grounds
Bad engine grounds may be caused by:
- Loose, rusted or damaged ground terminals or wires
- A loose, damaged or corroded ground battery terminal
- Poor component installation or repairs
Symptoms of a bad engine ground may include:
- Dim lights
- Flickering lights
- Electrical devices working erratically
- Faulty fuel pump
- Slipping or burned out AC compressor clutch
- Intermittent failure of sensors
- Damaged throttle or transmission cables
- Hard starting
- Dead battery
Often, bad grounds are relatively easy to diagnose and fix, usually in minutes. You can diagnose and make the repair in your own garage using just a digital multimeter (DMM) and some common tools.
If you don't know where all the engine or transmission grounds are located in your car, you may need to consult your vehicle repair manual. You can get a relatively inexpensive copy through Amazon. Haynes manuals come with step-by-step procedures for many maintenance, repair, and troubleshooting projects. So you'll get your small investment back in a short time.
OK. So get your multimeter and let's find those bad grounds in your vehicle.
I. Diagnosing Electrical Grounds
II. Checking Engine Grounds
III. Checking Chassis Grounds
IV. Checking Transmissions Grounds
V. Preventing Bad Ground Damage
I. Diagnosing Electrical Grounds
The following sections are divided between "engine ground" and "body ground" tests. This will make it easier to test the starter motor ground path and accessories grounds to find common electrical system problems.
Here are a couple of important points to keep in mind when troubleshooting grounds in your vehicle:
- When checking ground connections, make sure the terminals attach to a non-painted surface. You want to connect to bare metal. Paint, corrosion, greasy surfaces, frayed or broken wires, and loose connections are the main cause of bad automotive grounds.
- Some vehicles use a separate body ground wire, besides the main ground (black battery cable), that runs from the battery negative terminal to the chassis. This is for the headlights, accessories and other electronic equipment.
II. Checking Engine Grounds
The engine ground provides an electrical return path for the starter motor. A bad engine ground is a common problem leading to hard-starting and no-starting conditions.
The following test takes a voltage drop reading to locate unwanted resistance in the engine ground path.
Disable the ignition or fuel system to prevent the engine from starting during your tests.
If the ignition system is equipped with a distributor, you can disconnect the high tension cable from the distributor cap and ground it to the engine (bolt or bracket) using a jumper wire. On other systems, you can remove the fuel pump fuse. Consult your car owner's manual or vehicle repair manual to locate the fuse. You can also use a starter remote switch. Connect the switch to the control circuit terminals on the starter relay or solenoid.
- Set your DMM to DC Volts and choose a range as close as possible, but grater than, battery voltage. For example, 20 volts. Or choose the autorange function, depending on your particular multimeter features.
- Connect the meter's red lead to a clean surface on the engine, and the meter's black lead to the negative (-) battery post.
Have an assistant crank the engine for about five seconds, just enough to get a good reading.
You should get a reading of 0.2 volts or less. Consult your manufacturer's specifications in your vehicle repair manual, if necessary. Did you get a higher reading? There's some unwanted resistance in the ground circuit. To locate the problem, continue with the next steps.
- Move your meter's red lead to the main ground terminal, engine end side.
Have your assistant crank the engine while you take a voltage drop reading.
Repeat the previous two steps, moving your red lead to the terminal that connects the black, main ground, cable to the battery post. When you get a reading of about 0.2 volts or less, the unwanted resistance is located between this and the previous test point. Check for corrosion, broken or loose wires.
III. Checking Chassis Grounds
Electronic modules and many electrical components on the engine, transmission and passenger cabin use the chassis or firewall as an electrical common ground. This test checks for unwanted resistance at these points, including the secondary ground path between the battery and chassis, used by some older models. If necessary, consult your vehicle repair manual.
- Connect your meter's black lead to the battery ground post (-), and your meter's red lead to the firewall.
Have an assistant crank the engine for a few seconds.
You should get a voltage drop of 0.2 volts or less. If the voltage drop is higher, continue with the next steps.
Move your meter's red lead to the terminal on the firewall end of the secondary ground wire. Take a voltage drop reading.
If you get a reading higher than 0.2 volts, go on to the next step.
Move your meter's red test lead to the next terminal, connecting point, following the path back to battery ground. Take a voltage drop reading at each point.
When you get a reading of about 0.2 volts or less, the unwanted resistance is located between this and the previous test point. Check for corrosion, broken or loose wires.
Also, check voltage drop across ground straps that connect the engine to chassis, and the engine to the firewall.
IV. Checking Transmission Grounds
Transmissions on some vehicle models come equipped with chassis and/or firewall grounds for modules, sensors and solenoids. You can also check these grounds using your DMM.
- Check voltage drop between the transmission case and battery negative post. Voltage drop should be 0.2 volts or lower.
- Check individual chassis grounds by taking a voltage drop across each ground strap on the transmission. Voltage drop should be 0.2 volts or lower.
Clean, repair or replace transmission grounds as necessary. Remove grease, rust and paint from under ground terminals, or replace damaged ground straps.
Common Voltage Drop Values
Across a connection
Across a wire or cable
V. Why It's Important to Find and Fix Bad Grounds
Bad Engine Grounds can ultimately prevent the battery from charging properly, the car computer from getting the correct signals, cause the headlights from illuminating properly or at all, cause hard-starting issues and other faults.
Even more, bad engine grounds can also cause damage. If too much current tries to find proper ground unsuccessfully, it will choose an easy path through transmission components, transmission cable, throttle cable, wheel bearings and narrow ground wires, causing severe damage to these and other components.
Whenever you see signs of electrical failures, check your engine grounds.
The diagnostic tests outlined here are simple procedures you can conduct using a digital multimeter. And they'll save you time and money in a few minutes.
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: My ignition fuse blows every time I turn the key to start the vehicle, could a bad engine ground cause this?
Answer: The starter motor may be pulling too much current or there's a short between the ignition and the starter motor. Have the starter motor tested. You may need a diagram and a test light to check the circuit. If you can hear a click sound when turning the ignition key before the fuse blows, probably the relay is good. Check from the starter solenoid relay to the solenoid, and make sure the ignition switch connections are still good, and the switch itself is good.
Question: My car won't start, I've replaced the battery and the starter, any advice?
Answer: Make sure you got good spark and fuel pressure. Sometimes, a bad connection in the starting circuit may cause this problem as well. This other post may help:
© 2019 Dan Ferrell
Dan Ferrell (author) on August 29, 2020:
There might be too much resistance in the ground side, which is making it hot. You may want to check the ground wires and connections. This other post may help:
Brian on August 29, 2020:
85 Chevy Tioga RV Class C I have headlights front running lights no rear brake lights reverse lights running lights turn signals fuses are good strong battery will start and run white ground wire is hot
Dan Ferrell (author) on August 19, 2020:
Check for blown fuses. Before replacing any fuses make sure the short has been repaired. Then download diagnostic trouble codes and see the descriptions. If you still can drive the car, you can take it to any auto parts store and have them download the codes. Most stores will do it for free. Hope this helps.
Super Kha on August 18, 2020:
I have a 2018 Lexus is250. I open the middle console to fix the Radio and I shorted the electrical. ABS, PS, E brake and check engine Lights Came on. Also, no power to window switch. I think the ground wire have been compromised. Can someone give me more insight? I don’t know much about electrical.
Dan Ferrell (author) on July 21, 2020:
There could be a bad connection to the starter relay. Check the relay connector for a loose or faulty wire. The fact that you need to push the relay to make the engine start, gives a clue where the fault might be. You may be able to use a test light to trace voltage. Hope this helps.
Jarred23 on July 21, 2020:
I have a 2012 Ford e150 and the only way I can eat it to start is by turning the key to the run position then I have to go under the hood and push down on the starter relay....I replace the starter and put a new starter relay do you think it is possibly just a bad ground coming from the relay or starter itself?
Dan Ferrell (author) on July 14, 2020:
There seems to be bad or loose ground. It is affecting different electrical systems. If the problem seems to correct itself and then shows up unexpectedly, you are dealing with a loose, corroded, or dirty ground connection, most likely a bad engine ground, since your battery light is coming on too. If you have a friend that can help you do some simple diagnostic, this other post may help:
Dan Ferrell (author) on July 14, 2020:
There could be a bad or loose ground. This other post may help check engine grounds:
Jessica on July 14, 2020:
A 2011 Chrysler van I just bought is having electrical issues. The automatic doors act up, the ac acts up and the other day my speedometer and digital displays wouldn’t work along with the power doors, windows and lights. It only got that bad that one time but I also have 2 bad tire pressure sensors that they told me to fix myself and the battery warning light is on all the time now too, any idea how I can best communicate this to the auto dealers mechanic?
William wright on July 13, 2020:
2013 corolla.. Changed fuel pump .. Battery went dead tryin to start got a jump but tachometer started jumping. Could this be just a bad ground or battery thats keepin it from starting
Dan Ferrell (author) on July 02, 2020:
If an engine ground is not working, things can get hairy, specially on heavy load circcuits. It's better to fix the ground and try the recalibration again. I'm assuming they are following the service manual. If that's the issue and gets fixed, the HVAC should get working again. Hope this helps.
Mali Girl on July 02, 2020:
When my mehanic disconnected the battery to replace the starter on my 2002 Suburban the auto HVAC went out and it won't recallibrate. They've tried a bunch of things and nothing is working. I'm not sure what sequence they are trying, if they have the sensor plugged in when they do it, if doors are open but now they have found a severed ground wire and think that's why it's not calibrating. They are on day 4. Any thoughts, suggestions, etc would be greatly appreciated! It's 90° and I have dogs and need the air to work. Thank you!
Dan Ferrell (author) on January 13, 2020:
There could be several reasons for this, but a bad ground can cause communications issues with the PCM. Connect the ground and check with a scan tool, if necessary, for circuitry issues.
Dave Cornett on January 11, 2020:
I have a 2011 Toyota tundra and not four-wheel-drive will not engage when I looked underneath the truck I noticed a ground wire that was hanging from the transmission. I don’t know where the other end goes. Could this keep it from engaging?
Dan Ferrell (author) on July 29, 2019:
There could be a problem with the powertrain control module (PCM) itself or the harness (electrical open or short). You need to have it checked.
Shay aka papabear on July 28, 2019:
I have a 01 eclipes gt v6 im geting no spark . computer is reading a p1603 witch is saying i think bad ground to box. What should i do?