Engine Control Module: Testing and Inspection

Reading Diagnostic Trouble Codes
To read Diagnostic Trouble Codes (DTCs), use a scan tool.

Important: Never clear Diagnostic Trouble Codes unless the diagnostic instructs you to. Clearing DTCs will erase all Freeze Frame and Failure Records buffers. Clearing DTCs will also reset Maintenance Inspection flags that are used for emission testing stations. The emission testing station will not perform an emission test if the flags are reset. If for any reason the PCM memory is cleared (battery disconnect, using a scan tool or charging system malfunction) the diagnostics must be run to reset the flags.

Following Diagnostic Procedures
Since the PCM can have a failure which may affect only one circuit, following the diagnostic procedures under testing and inspection will determine which circuit has a problem and where it is.

PCM Related Problems
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 may be the reason:

^ There is a problem with the PCM terminal connections. The diagnostic table will say PCM connection or PCM. The terminals 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 Diagnosis by Symptom and make a careful physical inspection of all portions of the system involved.

^ Shorted solenoid, relay coil, or harness. Solenoid and relays are turned ON and OFF by the PCM using internal electric 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.