Electronic Control Module (ECM): Notes

NOTE: Some models use a Powertrain Control Module (PCM). The difference between an ECM and PCM is the PCM also controls electronic transmission internals and cruise control system. On 4.3L "S" and "T" series Pickup with manual transmission, a Vehicle Control Module (VCM) is used. The VCM provides control of the engine systems as well as the anti-lock brake system. Unless stated otherwise, references to ECM also apply to VCM and PCM-equipped vehicles.

ECM is located in passenger compartment. For exact location of ECM, see ECM LOCATION in appropriate TESTS W/CODES article in this section or under COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section. The ECM consists of the Arithmetic Logic Unit (ALU), Central Processing Unit (CPU), power supply and system memories.

The ECM has a "learning" ability which allows it to make minor corrections for fuel system variations. If battery power is interrupted, a vehicle performance change may be noticed. ECM corrects itself, and normal performance returns if vehicle is allowed to "relearn" optimum control conditions. "Relearning" occurs when vehicle is driven at normal operating temperature under part throttle, moderate acceleration and idle conditions.