boostboy76
Member
Found the following on an automtive DIY site, and thought it would make an excellent reference for anyone wanting to investigate a likely ground fault in their electrical system.
For example, my Magna was running like an absolute dog, stalling pulling up to the lights, "hopping", hunting through gears, not idling properly, etc.
Turned out to be a bad ground on the auto trans ecu, which about 3 mechanical / auto electrical places completely missed until I happened to find a place that was familiar with this issue on Magnas!
Anyhow, here it is:
Ground Diagnosis. [Tips from Mike Dale, Motor Magazine, Jan 01]
Many devices achieve their electrical connection to ground by way of a bolt or screw attached directly to the frame, body or drivetrain. As in the ring terminal example, the integrity of these grounds is dependent on the quality of the mechanical connection.
There are several basic problems inherent in achieving reliable grounding.
First, there's the issue of the mechanical connection itself. As an example, take the typical tin-plated brass ring terminal. This is crimped on one end of a wire to be grounded and fastened to the body by a self-tapping sheet-metal screw. Think of all the things that could go wrong with such a connection: The crimp to the wire could come loose, corrode or become mechanically damaged in a collision. The sheet-metal screw could back out as the body flexes during use and thermal cycling. The terminal and the place on the body to which it attaches could corrode due to salt, water or other corrosive fluids such as battery acids.
While identifying ground-related problems is not necessarily easy, there are some scenarios that should automatically raise a red flag. Multiple, seemingly unrelated failures are often ground-related issues. Mysteries such as the dome light flashing in unison with the turn signals are often fuse- or ground connection-related. Sensor outputs that are either out of range high or a constant value can be an indication of a ground problem. Poor performance of power loads such as the starting system, solenoids and fan motors may be the result of a poor ground connection, as well.
Analog sensors are much more susceptible to ground offsets and electrical noise in the system. The output of these sensors is often low (oxygen sensors, for example) and any loss due to poor connections can result in misinformation being sent to the computer.
Finding bad grounds is not always easy. Often, those sheet-metal screws I mentioned earlier can be buried in places that have never seen the light of day. Connections that look terrible may actually be okay, and vice versa. Just finding the location of a ground sometimes can be an all-day affair. Fortunately, much of the newer service literature does include ground location information.
Once you've found the connection point, there are a couple of things you can do to check ground integrity. One is to attach one lead of a DVOM to battery negative and the other lead to the ground lug, ring terminal or metal body of a grounded assembly. When you operate the device, there should be less than a 1-volt drop across the connection; 100 millivolts is better, especially if it's in a low-voltage computer circuit. You can do much the same with an ohmmeter if the circuit is not powered up. What you're looking for is pretty close to a zero resistance connection.
Straightening out a bad ground often can be accomplished by simply loosening a screw or a mounting bolt, then retightening it.
In those cases where the integrity of a ground remains in doubt, there is something else you can do as either a diagnostic technique or as a permanent solution-hook up a redundant ground. To do this, attach one end of a wire to a known-good grounding point, such as the vehicle body or the negative side of the battery. Then bring the opposite end to the body of the grounded part or to the ground terminal in the connector to that part. Assuming that the wire doesn't get tangled in some moving part, the very worst that can happen is that nothing will happen. If the problem really is a ground issue, the wire may confirm the diagnosis or, when properly secured, be a permanent solution.
The key to identifying and fixing ground problems is to remember what the ground system does. It provides the return path for power and information distribution and forms the reference that voltages are measured in relation to. When your diagnosis says that neither of those two things is happening, it's time to go hunting for that bad ground connection!
For example, my Magna was running like an absolute dog, stalling pulling up to the lights, "hopping", hunting through gears, not idling properly, etc.
Turned out to be a bad ground on the auto trans ecu, which about 3 mechanical / auto electrical places completely missed until I happened to find a place that was familiar with this issue on Magnas!
Anyhow, here it is:
Ground Diagnosis. [Tips from Mike Dale, Motor Magazine, Jan 01]
Many devices achieve their electrical connection to ground by way of a bolt or screw attached directly to the frame, body or drivetrain. As in the ring terminal example, the integrity of these grounds is dependent on the quality of the mechanical connection.
There are several basic problems inherent in achieving reliable grounding.
First, there's the issue of the mechanical connection itself. As an example, take the typical tin-plated brass ring terminal. This is crimped on one end of a wire to be grounded and fastened to the body by a self-tapping sheet-metal screw. Think of all the things that could go wrong with such a connection: The crimp to the wire could come loose, corrode or become mechanically damaged in a collision. The sheet-metal screw could back out as the body flexes during use and thermal cycling. The terminal and the place on the body to which it attaches could corrode due to salt, water or other corrosive fluids such as battery acids.
While identifying ground-related problems is not necessarily easy, there are some scenarios that should automatically raise a red flag. Multiple, seemingly unrelated failures are often ground-related issues. Mysteries such as the dome light flashing in unison with the turn signals are often fuse- or ground connection-related. Sensor outputs that are either out of range high or a constant value can be an indication of a ground problem. Poor performance of power loads such as the starting system, solenoids and fan motors may be the result of a poor ground connection, as well.
Analog sensors are much more susceptible to ground offsets and electrical noise in the system. The output of these sensors is often low (oxygen sensors, for example) and any loss due to poor connections can result in misinformation being sent to the computer.
Finding bad grounds is not always easy. Often, those sheet-metal screws I mentioned earlier can be buried in places that have never seen the light of day. Connections that look terrible may actually be okay, and vice versa. Just finding the location of a ground sometimes can be an all-day affair. Fortunately, much of the newer service literature does include ground location information.
Once you've found the connection point, there are a couple of things you can do to check ground integrity. One is to attach one lead of a DVOM to battery negative and the other lead to the ground lug, ring terminal or metal body of a grounded assembly. When you operate the device, there should be less than a 1-volt drop across the connection; 100 millivolts is better, especially if it's in a low-voltage computer circuit. You can do much the same with an ohmmeter if the circuit is not powered up. What you're looking for is pretty close to a zero resistance connection.
Straightening out a bad ground often can be accomplished by simply loosening a screw or a mounting bolt, then retightening it.
In those cases where the integrity of a ground remains in doubt, there is something else you can do as either a diagnostic technique or as a permanent solution-hook up a redundant ground. To do this, attach one end of a wire to a known-good grounding point, such as the vehicle body or the negative side of the battery. Then bring the opposite end to the body of the grounded part or to the ground terminal in the connector to that part. Assuming that the wire doesn't get tangled in some moving part, the very worst that can happen is that nothing will happen. If the problem really is a ground issue, the wire may confirm the diagnosis or, when properly secured, be a permanent solution.
The key to identifying and fixing ground problems is to remember what the ground system does. It provides the return path for power and information distribution and forms the reference that voltages are measured in relation to. When your diagnosis says that neither of those two things is happening, it's time to go hunting for that bad ground connection!
