Computers and Control Systems: Description and Operation

Control Module System:

Control Module - Block Diagram:

PURPOSE
At the heart of the Computer Command Control System (C3) is a Control Module. The control module with the help of input sensors, can monitor a number of engine, transmission and vehicle operating functions to maintain compliance with exhaust emission levels while providing good driveablity and fuel efficiency.

DESCRIPTION
General Motors Corporation uses the following control modules:
- Engine Control Module (ECM) - controls engine system and [1][2]torque converter clutch on non-electronic automatic transmission or shift lamp on manual transmissions.
- Powertrain Control Module (PCM) - controls engine system automatic transmission shift functions or shift lamp on manual transmissions.
- Vehicle Control Module (VCM) - controls engine system, electronic brake control functions and shift lamp on manual transmissions.

OPERATION
Control Module Controlled Systems:
- Fuel Delivery (EFI)
- Ignition Control (IC)
- Knock Sensor (KS) system
- Air Injection (AIR) system
- Exhaust Gas Recirculation (EGR)
- Evaporative Emission System (EVAP)
- Air Conditioning Status
- Coolant Fan
- Engine Speed
- Transmission Functions
- Rear Wheel Antilock Brake System (ABS)


Self Diagnostics and "SERVICE ENGINE SOON" light:
The C3 system has a built-in diagnostic system that recognizes and identifies possible operational problems. The C3 system signals the driver through a "SERVICE ENGINE SOON" light located on the instrument panel. The "SERVICE ENGINE SOON" light will remain "ON" until the problem is identified and repaired. This same light is combined with the built-in diagnostic system in order to assist the technician in locating and correcting problems within the C3 system. It does this by flashing a series of codes which identify the possible problem areas at fault, within the C3 system. The system also allows for near normal driving conditions, during system malfunction, through the use of the built-in backup system. The backup system remains in effect until repairs can be made.