Engine Control Module: Description and Operation

Powertrain Control Module:

DESCRIPTION
The Powertrain Control Module (PCM) is located in the passenger compartment and is the control center of the control module system.
The PCM constantly interprets the information from various sensors, and controls the systems that affect vehicle performance and performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL) "Service Engine Soon" and store a Diagnostic Trouble Code (DTC) which identify the problem areas to aid the technician in making repairs. Refer to diagnosis section for further information.
The PCM is designed to process the various input information and then send the necessary electrical responses to control fuel delivery, spark timing, and other emission control systems. The input information has an interrelation to more than one output, therefore, if the one input failed it can affect more than one system's operation.

PROM (MEM-CAL)
This assembly contains the calibrations needed for a specific vehicle, as well as the back-up fuel control circuitry required if the rest of the PCM becomes damaged or faulty.

PCM LEARNING ABILITY
The PCM has a "learning" ability which allows it to make corrections for minor variations in the fuel system to improve driveability. If the battery is disconnected, to clear diagnostic trouble codes or for other repairs, the "learning" process resets and begins again. A change may be noted in the vehicle's performance. To "teach" the vehicle, ensure that the engine is at operating temperature. The vehicle should be driven at part throttle, with moderate acceleration and idle conditions until normal performance returns.


CAUTION: The PCM must be maintained at a temperature below 85°C (185°F) at all times. This is most essential if the vehicle is put through a paint baking process. The PCM will become inoperative if its temperature exceeds 85°C (185°F). It is recommended that temporary insulation be placed around the PCM during the time the vehicle is in a paint oven or other high temperature processes.