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Old 04-08-2012, 07:50 AM
 
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I often hear people say check your ground when they talk about an automotive problem. Being inexperienced I have no idea what this means. Does this mean a ground cable is loose? A ground cable is shorted to something else? How does it cause a engine to stall, a component to fail, etc.?

I would appreciate very much if someone can explain what a ground problem is and how it affect engine performance. Thank you.
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Old 04-08-2012, 08:12 AM
 
Location: My little patch of Earth
5,160 posts, read 2,018,701 times
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Quote:
Originally Posted by davidt1 View Post
I often hear people say check your ground when they talk about an automotive problem. Being inexperienced I have no idea what this means. Does this mean a ground cable is loose? A ground cable is shorted to something else? How does it cause a engine to stall, a component to fail, etc.?

I would appreciate very much if someone can explain what a ground problem is and how it affect engine performance. Thank you.
Ground circuit problems are the plague of electronics. Loss of ground can cause a plethora of different seen and unseen issues.

When the ground circuit termination is loose (cable, connector, etc.) amperage draw becomes excessive on the device that is served by that ground. The result is heat and shortened life. If completely broken the other ground circuits in the system will provide some current flow but then again, heat and shortened life of the device can occur. It doesn't always due to the engineers designing in an over amperage protection. Not every device has this protection.

Loss of function and performance is a direct result of loss of proper grounding. If the devices cannot get the proper flow of electricity (amps, volts, duty cycle, etc.) that device cannot perform at it's peak design.

Ground circuits can and do short to other circuits if not protected in some way. In the same way the power circuit must be protected the ground must be also. Consider if a power and ground circuit shorted (touched) BEFORE the device the result would be a spark. The fuse or breaker SHOULD do it's job but....sometimes burnt wires can be the result and the device can be destroyed as well. If the ground is shorted after the device to anything other than another ground wire, the device's performance is greatly affected. From static in speakers, to a light that will not turn off when intended, to poor performance.

Electrical energy is exactly like water under pressure and it's also completely different. It wants to flow. Hard to compare or explain. And it's really a bad analogy that others will decry. But it is what it is.

Electronics and electricity are very simple. Until of course something is not right and then it's very complicated.
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Old 04-08-2012, 08:27 AM
 
Location: Northern MN
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In this example the drain pipe is the ground.

Think if it as your toilet is plugged up. You flush to try and get rid of the toilet paper but there is to much. So, not only does it back up the paper but the water has a very hard time going anywhere.

clean drain, clean ground and it will flow
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Old 04-08-2012, 09:37 AM
 
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Is ground the same for everything in a car since all ground cables are attached to the chassis and the engine block?
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Old 04-08-2012, 09:44 AM
 
Location: Northern MN
3,870 posts, read 5,266,005 times
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Your making me type..



Essentially, a "ground" is an electrical connection to a common return in circuit. In automotive terms a ground is a connection to the body or other metal surface of the vehicle. The body is connected to the negative terminal of the battery. Thus any connection to the body of the car is a connection to the negative terminal of the battery.
Electricity flows from the positive of the battery, through the circuit to do some work, then back through the body to the battery . This is a "negative ground" system which is by far the most popular automotive ground scheme used in the automotive world.

The main reason this is done is to greatly simplify the wiring of a vehicle. Since most car bodies are made of metal (at the very least almost all frames are) they provide a perfect ground plane, eliminating the need to run a separate ground wire to each circuit which almost chops the amount of wire necessary in half.


Good grounds are important because poor grounds cause voltage drop. The consequence of this voltage drop is that the systems in that circuit can malfunction. How do bad grounds cause voltage drop? Well, the answer is Ohms Law.
Ohm's Law states that V=IR. This means that the voltage drop (V) is proportional to the current through the circuit (I) and the resistance (R) of the resistor (or bad ground in our case). An easy example is attempting to draw 10 amps through a bad ground with a resistance of 1 Ohm. So V=10(1) thus making the voltage drop a whopping 10V. This leaves only 2 volts available (in a standard automotive 12V system) to power the circuit and means that all that extra power must be dissipated as heat at the resistor (bad ground). Generally this heat makes the condition even worse, causing more voltage drop and more heat. In the most severe cases the ground will function under light loads yet fail under high current draws causing what appears to be an intermittent failure. Many people have seen this behavior caused by a loose (high resistance) battery terminal.

Bad grounds can cause poor performance in almost any circuit. Voltage drop can manifest itself as dim headlights, one circuit malfunctioning when another is switched on (a common symptom is that the heater blow slows and dash lights dim when the brake pedal is pressed) and all kinds of other random weird issues.
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Old 04-08-2012, 10:35 AM
 
1,892 posts, read 3,620,321 times
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Thank you so much for the explanation. Wish I could give you more rep points.

Does each circuit in a car have its own ground cable? Can two or more circuits share a common ground cable? If a circuit has a ground problem, is the cause the ground cable for that circuit only? Or can a bad ground cable in another circuit be the cause?
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Old 04-08-2012, 10:43 AM
 
8,286 posts, read 22,030,562 times
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Quote:
Originally Posted by davidt1 View Post
Thank you so much for the explanation. Wish I could give you more rep points.

Does each circuit in a car have its own ground cable? Can two or more circuits share a common ground cable? If a circuit has a ground problem, is the cause the ground cable for that circuit only? Or can a bad ground cable in another circuit be the cause?
Depending upon the device being powered, it can have it's own grounding circuit/cable or it can be a common circuit. Examples could be the ground wire from a computer to the chassis, or the main frame ground wire from the battery to the chassis.

If a circuit has a ground problem, it can be unique to that particular item or it can also cause feedback to other grounds or circuits and affect them. So, yes, a bad ground cable can cause problems in other circuits.
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Old 04-08-2012, 11:35 AM
 
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It is the same problem as with an electrical outlet in your house where you need to "jiggle" the plug to get it to work or "bend the prongs" on the plug to get it to work. A poor connection. (Of course the proper way to fix that problem is to replace the outlet.)

And same with a car. The only thing is with a car, to save money, they use a "trick" for a lot of the wiring. The entire car is metal, so they attach the negative connection from the battery to the metal of the engine and the body.

Then they just need to run 1 wire (positive) to everything. The other connection is to a nearby screw going into the metal body or engine.

So you might see a fog light with one wire going to it and the other wire going to a screw in the metal body.

Or there may be one wire going to the temperature gauge sensor. The other connection is where the sensor screws into the metal engine.

Or a spark plug has just one wire, the other connection is via the screw threads going into the metal engine.

With that said, there are large wires going from the battery negative terminal to the engine and body. That connection might be poor at the battery, or loose and dirty where it connects to the engine or body. Or the wire might be damaged and not able to carry the full load.

Thus 1/2 of the electrical circuit is not making a good connection.

Also where devices like headlights, etc. connect to the engine or body, that connection might be loose or dirty.

You can troubleshoot these problems with a "voltage drop test" using a multimeter. Search google.com for the words...

automotive voltage drop test
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Old 04-08-2012, 12:14 PM
 
Location: Not far from Fairbanks, AK
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This is one of numerous very simple ways to explain it:

a. Every electrical component in you car, even a light bulb, has to have a negative and a positive connection to the battery for it to work. The negative pole (-) of your battery is connected to the chassis of your vehicle, and this is the ground you are referring to.

b. Lets say that you have a lightbulb in your car. For this lightbulb to energize (turn ON), it must be connected to both the positive and the ground side of your vehicle. Remember that the negative pole is connoted to the chassis of you vehicle, and that this chassis is the "ground" side.

c. So, one lead or wire is connected to the positive side of the battery, and the other lead is connected to the vehicle's chassis. However, since the metallic frame (ribs, etc.) of your vehicle is grounded to the chassis, you can have grounding points throughout the vehicle. Even the motor is grounded to the chassis via a grounding strap. The electricity that powers all of the electrical components in your vehicle travels out the positive side of the battery, through each electrical component, then through the chassis and ground points, back into the battery through the negative pole.

d. If a grounding strap, or any grounding point is loose, the electrical components affected can't work because the circuit is broken (open). In your case a "ground problem" could be a loose, or corroded, or broken ground wire or grounding point. Since the ground lead (wire) usually has a wire terminal, check this terminal to make sure it's clean and secure on the grounding area.

Last edited by RayinAK; 04-08-2012 at 12:36 PM..
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Old 04-08-2012, 12:37 PM
 
3,997 posts, read 3,373,814 times
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My buddy rolled his Escalade into a ditch once, I thought that might qualify as a ground problem!
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