Engine Control Module: Testing and Inspection

The approved procedure for diagnosing all powertrain control system faults is included in the Strategy Based Diagnostic Flow The preliminary checks and the Powertrain On-board Diagnostic System Check must be performed to successfully diagnose and repair the powertrain systems. To read and clear diagnostic trouble codes, use a scan tool.

Important: Use a scan tool to clear diagnostic trouble codes from the PCM memory. Diagnostic trouble codes can also be cleared by turning OFF the ignition and disconnecting the battery power from the PCM for 30 seconds, but this method will also cause all diagnostic information in the PCM memory to be cleared and all the diagnostic tests will have to be re-run.

Since the PCM can have a failure which may affect only one circuit, following the approved diagnostic procedures will determine which circuit has a problem and where it is. If a diagnostic table indicates that the PCM connections or PCM is the cause of a problem and the PCM is replaced, but does not correct the problem, one of the following conditions may exist:

There is a problem with the PCM terminal connections. The diagnostic table will indicate that the PCM connections or PCM is the problem. The terminals may have to be removed from the PCM connector in order to check them properly.

^ The EEPPOM program is not correct for the application.

^ Incorrect components may cause a malfunction and may or may not set a DTC.

^ The problem is intermittent. This means that the problem is not present at the time the system is being checked. In this case, refer to the Symptoms portion of the manual and make a careful visual and physical inspection of all suspected components and wiring associated with the affected system.

^ Shorted solenoid, relay coil, or harness. Solenoids and relays are turned ON and OFF by the PCM using internal electronic switches called drivers. Each driver is part of a group of seven called output driver modules. A shorted solenoid, relay coil, or harness will not damage the PCM but will cause the solenoid or relay to be inoperative. The J 34636 tester, or equivalent, provides a fast, accurate means of checking for a shorted coil or a short to battery voltage.

MIL Requests and History Codes
The Diagnostic Executive must acknowledge when all the emissions related diagnostic tests have reported a pass or fail condition since the last ignition cycle. Each diagnostic test is separated into 4 types:

^ Type A - Emissions related, turns on the MIL the first time the diagnostic executive reports a fault.

^ Type B - Emissions related, turns on the MIL if fault is active for 2 consecutive driving cycles.

^ Type C - Non-emissions related, does not turn on the MIL but will turn on the service light.

^ Type D - Non -emission related does not turn on MIL or the service light.

When a type A diagnostic test reports a failure, the Diagnostic Executive immediately requests to have the MIL turn on for that diagnostic test. When a type B diagnostic test reports a failure during 2 consecutive trips, the Diagnostic Executive turns on the MIL for that diagnostic test. The Diagnostic Executive has the option of turning the MIL off when the diagnostic test which caused the MIL to illuminate passes for 3 consecutive trips. In the case of misfire or fuel trim malfunctions, there are additional requirements as follows:

^ The load conditions must be within 10% of the vehicle load present when the diagnostic executive reported the failure.

^ The engine speed conditions must be within 375 RPM of the engine speed present when the diagnostic executive reported the failure.

^ The engine coolant temperature must have been in the same range present when the diagnostic executive reported the failure.