Engine Control Module (ECM): Diagnosis

Since the ECM can have a failure which may affect only one circuit, following the DIAGNOSTIC PROCEDURES  can reliably tell when a failure has occurred in the ECM. Poor engine performance, idle or part throttle surges, loss of cruise control, a flashing "Engine Control System Fault" telltale, no starts, and/or hard starting may be experienced by a poorly seated MEM-CAL unit. If the MEM-CAL unit is missing, a code B334 will set and the car will not start. Refer to BODY COMPUTER MODULE article in COMMUNICATION DEVICES.

Service of the ECM should normally consist of either replacement of the ECM or a MEM-CAL change. If the diagnostic procedures call for the ECM to be replaced, the Memory-Calibration unit (MEM-CAL) and ECM should be checked first to see if they are the correct parts. Also, perform the "PFI CHART C-1: ECM REPLACEMENT CHECK  " in this article before replacing an ECM to assure that the replacement ECM will not be damaged.

The PROM can easily be checked using parameter ED99. If the part numbers are correct, remove the MEM-CAL from the faulty ECM and install them in the new service ECM. The service ecm will not contain A MEM-CAL, so care should be taken when removing the MEM-CAL from a defective ECM which is being replaced. Trouble Code B334 (No ECM Data) indicates the MEM-CAL is installed improperly or has malfunctioned. If Code B334 is current, check to see if the MEM-CAL is fully seated. If not fully seated, press firmly on the ends of the MEM-CAL and make sure the retaining clips have locked.

If the MEM-CAL is installed correctly and Code "B334" still shows, diagnose using the procedure outlined in DTC B334: LOSS OF ECM DATA in BODY COMPUTER MODULE article in COMMUNICATION DEVICES. After replacement of an ECM, clear stored codes, and check the vehicle for proper operation.