Engine Control Module: Testing and Inspection

To read diagnostic trouble codes, use a Tech 1 tool. To clear diagnostic trouble codes from memory:

^ Ignition "OFF."
^ Disconnect PCM power source for 30 seconds.

OR

^ Diagnostic trouble codes may be cleared with the Tech 1 scan tool.

Since the PCM can have a failure which may affect only one circuit, following the diagnostic procedures in this section will determine which circuit has a problem and where it is.

If a diagnostic chart 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 chart will say PCM connections or PCM. To check for an oversize terminal, use a #62 drill bit (shank of drill bit must first be measured to ensure proper diameter of 0.038 inches, .965 mm). Place a flag made of tape 1/2 inch up from the bottom of the shank of the drill bit. Remove connector from PCM and while holding connector up vertically, place the #62 drill bit into the suspect terminal (do not push on drill bit). Replace any terminal allowing the drill bit to fall unassisted to the flag of the drill bit.

^ PROM 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 Diagnosis by Symptom and make a careful physical inspection of all portions of the system involved. Testing and Inspection

^ 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 four called "Quad-Drivers."

A shorted solenoid, relay coil, or harness will not damage the PCM but will cause the solenoid or relay to be inoperative. J-34636 or BT-8405 testers, or equivalent, provide a fast, accurate means of checking for a shorted coil or a short to battery voltage.

^ The PROM may be faulty, although these rarely fail, it operates as part of the PCM. Therefore, it could be the cause of the problem. Substitute a known good PROM.

^ The replacement PCM may be faulty. After the PCM is replaced, the system should be rechecked for proper operation. If the diagnostic chart again indicates the PCM is the problem, substitute a known good PCM. Although this is a rare condition, it could happen.

PROM
An incorrect or faulty PROM, which is installed in PCM, may set DTC P1623. Testing and Inspection