Computers and Control Systems: Description and Operation

ECM And Connector:

ECM Inputs And Outputs:

Purpose:
The Computer Command Control System uses a Powertrain Control Module (PCM) which monitors a number of engine and vehicle operating conditions and controls the following systems:

^ Fuel Delivery
^ Ignition/Electronic Spark Timing (EST)
^ Electronic Spark Control (ESC)
^ Air management
^ Air Conditioning Compressor Clutch
^ Engine Cooling Fans
^ Idle Speed (IAC Valve)
^ Evaporative Emission Control Purge
^ Exhaust Gas Recirculation (EGR)
^ 1-4 Upshift System
^ ASR Timing Retard (Traction Control)
^ Secondary Port Throttle Valve System (Power Mode)

Operation:
The computer has a built-in diagnostic system that recognizes and identifies malfunctions in certain devices and circuits.

When a malfunction is detected, the vehicle operator is notified by the "Malfunction Indicator Light" or MIL, located on the instrument panel. The MIL will turn "ON" if a problem is detected in a monitored device or circuit, and remain "ON" until the problem is repaired. Diagnostic Trouble Codes (DTCs) can be displayed through the MIL which identify the system, device, or circuit where a malfunction has been detected. Codes are displayed when the diagnostic test terminal of the Assembly Line Data Link (ALDL) is grounded.

The system also has a "fail-safe mode that allows for near normal vehicle operation during some system malfunctions. Once the system is in fail-safe mode, it will remain in that mode as long as the problem is present. The PCM will continue monitoring the sensors and outputs and will return to normal closed loop operation if the problem goes away (intermittent.)