Computers and Control Systems: Description and Operation

SYSTEM DESCRIPTION
This vehicle is equipped with a computer controlled engine management system that electronically controls fuel injection, ignition, and emission control systems. The Powertrain Control Module (PCM) is the central computer for engine systems management. It monitors several engine/vehicle operating conditions, processes the information, and operates various engine performance and emission control related systems. For the catalytic converter to operate efficiently, the air/fuel mixture must be maintained close to the ideal ratio of about 14.7:1 by mass. The computer system keeps the air/fuel ratio very close to the ideal stoichiometric ratio, varying several times per second between slightly rich and slightly lean.

The system has built-in self diagnostics that can identify possible operational problems, and notify the driver through the Malfunction Indicator Light (MIL or SERVICE ENGINE SOON Light) located on the instrument panel. The MIL light will turn "ON" if a fault is detected in a monitored system, and remain "ON" as long as the problem is pressent. If the problem is related to a computer controlled emission control device, or is otherwise emission related, the MIL light will remain "ON" until the problem is corrected and the computer memory cleared. This same light is used with the built-in diagnostic system in order to assist the technician in locating and correcting problems within the system. It does this by flashing a series of codes which identify the problem circuits or devices where the fault was detected.

The system also allows for near normal driving conditions during system malfunction, through the use of a built-in backup system. In the event of a computer related failure in a critical system, the backup system will take over base functions and remain in effect until repairs can be made, so the vehicle can still be driven. For detailed information of the computer, sensors and controlled devices, refer to COMPUTERS AND CONTROL SYSTEMS.