Engine Control Module: Description and Operation

Powertrain Control Module (PCM):

Purpose:
The ECM constantly receives information from various sensors and performs diagnostic functions of the system. The ECM recognizes operational problems and alerts the driver through the "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR" light. It stores trouble codes which identify the problem area to diagnose and repair.

The computer is designed to process various input information, and send the necessary electrical response to control fuel delivery, spark control, and other emission control systems.



Operation:
The ECM can control these devices through the use of Quad Driver Modules (QDM). When the ECM is commanding a device or a component "ON," the voltage potential of the output is "LOW" or near zero volts. When the ECM is commanding a device or component "OFF," the voltage potential of the circuit will be "HIGH," or near 12 volts. The primary function of the QDM is to supply the ground for the component being controlled.

The computer 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 trouble codes or for repair, the learning process has to start over. A change may be noticed in the driving performance of the vehicle. To reset the vehicles learning ability, make sure the engine is at operating temperature and operate the vehicle at part throttle, moderate acceleration, and idle conditions, until normal performance returns.



Location:
The Electronic Control Module (ECM) is located in the passenger compartment.