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Diagnosing the Symptoms of a Bad Engine Ground

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Locate the engine grounds on your vehicle.

Locate the engine grounds on your vehicle.

Bad Engine Ground

Checking for bad grounds is a good starting point when you are having car electrical issues, including trouble codes pointing to one or more sensors. Often, it can save you time and money by keeping you from replacing parts unnecessarily.

Bad grounds can cause one or more circuits to come alive when they shouldn't; for example, lights that illuminate on their own, even when the switch is off.

An electrical circuit needs a good ground to function correctly. A bad electrical ground may affect one or more electrical systems because it forces the current to search for other easy paths back to the 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
  • No-starting
  • Dead battery
  • Introduce radio noise
  • Ignition coil failure

And the list goes on. A faulty ground is often the cause of these problems. However, 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.

Index

I. Diagnosing Electrical Grounds

II. Checking Engine Grounds

III. Checking Chassis Grounds

IV. Checking Transmissions Grounds

V. Starter Motor Slow Cranking or No Cranking

VI. Preventing Bad Ground Damage

Corroded or damaged ground straps can cause electrical accessories to fail.

Corroded or damaged ground straps can cause electrical accessories to fail.

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 accessory 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.
You can use a remote starter switch to crank the engine when testing grounds in your vehicle. Connect the switch to battery power and the "s" terminal on your starter solenoid or the remote starter relay.

You can use a remote starter switch to crank the engine when testing grounds in your vehicle. Connect the switch to battery power and the "s" terminal on your starter solenoid or the remote starter relay.

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.

  1. 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.

  2. Set your DMM to DC Volts and choose a range as close as possible, but greater than, battery voltage. For example, 20 volts. Or choose the autorange function, depending on your particular multimeter features.
  3. Connect the meter's red lead to a clean surface on the engine, and the meter's black lead to the negative (-) battery post.
  4. 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.

  5. Move your meter's red lead to the main ground terminal, engine end side.
  6. 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.

Replace chassis grounds as necessary.

Replace chassis grounds as necessary.

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.

  1. Disable the ignition or fuel system to prevent the engine from starting. See point #1 in the previous section, if necessary.
  2. Set your transmission to Neutral (manual) or Park (automatic).
  3. Connect your meter's black lead to the battery ground post (-), and your meter's red lead to a clean spot on the engine block, cylinder head, or bolt.
  4. Have an assistant crank the engine for a few seconds.
  5. You should get a voltage drop of 0.2 volts or less. If the voltage drop is higher, check engine ground connections and ground wires between the engine and battery ground and chassis. Fix grounds as necessary.
  6. Now, enable the ignition or fuel system.
  7. Start the engine and let it idle.
  8. Turn on major electrical accessories like headlights, wipers, heater blower and auxiliary lamps.
  9. Connect your meter's black lead to the battery negative terminal, and your meter's red lead to the firewall.
  10. You should get a voltage drop of 0.2 volts or less.
  11. If your voltage drop is higher, check voltage drop across ground straps that connect the engine to the chassis, and the engine to the firewall. Fix connectors or wires as necessary.
Search, test and replace transmission grounds as necessary.

Search, test and replace transmission grounds as necessary.

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.

  1. Check voltage drop between the transmission case and battery negative post. The voltage drop should be 0.2 volts or lower.
  2. Check individual chassis grounds by taking a voltage drop across each ground strap on the transmission. The voltage drop should be 0.2 volts or lower.

Clean, repair or replace transmission grounds as necessary. Remove grease, rust and paint from underground terminals, or replace damaged ground straps.

Common Voltage Drop Values

Across a connection

0.00 volts

Across a wire or cable

0.2 volts

Throttle cables and other equipment can suffer damage when high electrical current can't find the proper path back to ground.

Throttle cables and other equipment can suffer damage when high electrical current can't find the proper path back to ground.

V. Starter Motor Slow Cranking or No Cranking

A bad grounded starter motor or fault ground connection can also cause the starter motor to crank slowly or not at all.

Make sure the starter motor case is making tight and clean contact with the engine. Then, check the starter motor voltage drop.

  1. Disable the ignition system or fuel system to prevent the engine from starting. If your engine has a distributor, disconnect the high tension, ignition coil lead from the distributor cap and ground the lead with a jumper wire; or remove the fuel pump fuse.
  2. Set your voltmeter to a flow volt setting on the DC Volt scale.
  3. Connect the black meter's lead to the negative battery post, and the meter's red lead to the starter motor case.
  4. You should get a voltage drop of 0.1 volts or less.
  5. Now, have an assistant crank the engine for about 5 seconds.
  6. You should get a voltage reading of 0.5 volts or less.
  7. If a voltage drop reading exceeds the specification, check for a bad grounded starter motor, or a bad ground cable or connection. Move your red meter's lead to the battery ground terminal on the engine block; then to the terminal connected to the battery. Whenever you get a good voltage drop reading, your problem is between this spot and the previous one.

Check other engine and chassis grounds as necessary.

VI. Why It's Important to Find and Fix Bad Grounds

Bad engine grounds can ultimately prevent the battery from charging properly, prevent 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:

https://axleaddict.com/auto-repair/How-to-Use-Volt...

© 2019 Dan Ferrell