Electronic Control Module (ECM): Notes

NOTE: Some models use a Powertrain Control Module (PCM) instead of an Electronic Control Module (ECM). The only difference between an ECM and PCM is the PCM controls electronic transmission internals and cruise control system in addition to electronic engine controls. Unless specifically stated, references to ECM also apply to PCM-equipped models.

On most vehicles, ECM is located in passenger compartment. For location of ECM, see ECM/PCM LOCATION in appropriate G - TESTS W/ CODES article in this section, or refer to COMPONENT LOCATIONS in appropriate I - SYS/COMP TESTS article in this section. The ECM contains 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 to ECM is interrupted, a vehicle performance change may be noticed. This will correct itself and normal performance will return if vehicle is allowed to "relearn" optimum control conditions. This is accomplished by driving vehicle at normal operating temperature, under part throttle, moderate acceleration and idle conditions.