Diagnosing Electrical Engine Control Systems

Diagnosing electrical engine control systems involves much more than accessing the stored trouble codes in the computer memory. As is true during diagnosis of any system you need to know what to test when to test it and how to test it.

Picture of diagnosing engine codes

Diagnosing engine codes

Because the capabilities of the engine control computer have evolved from simple to complex it is important to learn everything you can about the system the set trouble code refers to before attempting to diagnose a specific problem. Referring to a vehicle specific service manual for this information is highly recommended.

After you have studied and completely understand the system and its capabilities you can then begin your diagnosis using basic and logical methods. I cannot over emphasize the importance of logical troubleshooting. The ability to diagnose a problem that will lead you to the cause of the malfunction and its eventual solution is what separates an automotive technician from a parts changer.


Using logical diagnosis

When faced with abnormal engine conditions such as rough running or engine stalling the best automotive technicians compare clues with their knowledge of the system or circuits and formulate a logical path of diagnosis. This is similar to a ladder diagram in an auto repair manual.

In short this means following the most simple and basic procedures. Starting with the most likely cause and working towards the most unlikely cause. In other words check out the easiest most obvious solutions first before proceeding to the less likely ones.

The more you jump around from place to place the less likely you are to uncover the problem in a timely manner unless you are extremely lucky which I am not. Try not to guess at the problem or jump to conclusions before considering all the factors involved.

Often it is the logical approach that will solve even the most complicated electrical and electronic engine control problems. You also want to remember to check all of the traditional nonelectric engine control possibilities before attempting to diagnose the more complicated electrical side of the engine control systems itself.

Isolating problem areas

Determining which part of the computerized engine control system is defective requires having a thorough knowledge of how the system works as mentioned above. As an example if we say electronic engine control problems can most often be caused by defective sensors and sometimes defective output devices and in rare cases the computer itself.

The logical troubleshooting procedure would then be to check the input sensors and wiring first, and then the output devices and their wiring, and finally the computer last. Most late model computerized engine controls have self-diagnostic capabilities built-in. A malfunction in any sensor or output device including the computer itself should (not always) store a trouble code in the computer’s memory.

Picture of auto scanner

Auto Scanner

These stored codes can be retrieved and indicate the problem areas that will need to be checked further. As an example if you have set a code P0306 this is a code for an engine misfire isolated to the number six cylinder. This set code has narrowed your diagnosis down to focus only on the number six cylinder. You can now turn all of your attention to the problems that may cause a misfire on the number six cylinder.

Things like a bad coil pack a failed sparkplug or defective ignition wires are not only the easiest things to check first but also would be the most common problems that would set this code. The power of logical diagnosis can solve many automotive problems.

If you are thinking about purchasing some tools to get the job done I have a recent review of the new release Actron auto scanner. This next link will take you back to the auto repair blog from this page about diagnosing electrical engine control systems.


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