Engine Control Module: Description and Operation

Powertrain Control Module (PCM):

PURPOSE
The PCM constantly receives information from various sensors and performs the diagnostic functions of the system. It recognizes operational problems and alerts the driver through the "SERVICE ENGINE SOON" light.

The PCM stores trouble codes which identify the problem area to diagnose or repair. It is designed to process the various input information, and send the necessary electrical response to control fuel delivery, spark control, and other emission control systems.


OPERATION
The input information has an interrelation between sensor output. If one of the input devices failed, such as the oxygen sensor, this could affect more than one of the systems controlled by the computer.

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 begin all over again, and 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 Powertrain Control Module (PCM) is located in front of the drivers side engine compartment, under air cleaner assembly.