If you are reasonably certain that the problem is related to a particular electronic control system, the first step is to check for any stored trouble codes in that controller.
On vehicles with more than one vehicle controller (i.e., PCM, BCM, MIC, TCM, etc.), if you are unsure whether the problem is Powertrain related, start by checking for codes in the other controllers to determine if the problem is related to another vehicle system.
If there are no codes set, and you are certain which Powertrain subsystem has a problem, you can start by checking one of the subsystems. The subsystems include the Charging, Cooling, Fuel, Ignition and Speed Control systems.
If a wiring problem is found during testing, you will need to refer to wiring diagrams in the appropriate information resource. Using a wiring schematic can help you determine:
Once you decide how to repair the vehicle, in addition to performing the repair, it is a good idea to clear any trouble codes that were set and to verify they do not reset.
To verify a repair, you should confirm that the Check Engine Light is operational and goes out after the 4-second key-on bulb check. Then, you need to duplicate the conditions present when the customer complaint occurred or when a trouble code set; these are the actual code conditions that caused a code to set. The individual code conditions and possible causes are included under Section 3. You can use this information to find out how to drive a vehicle for problem verification.