Engine Control Module: Description and Operation

Control Module System:

Control Module - Block Diagram:

PURPOSE
The control module is the control center of the fuel injection system. The control module constantly looks at the information from various sensors (inputs) and controls a number of engine, transmission and vehicle operating functions to maintain compliance with exhaust emission levels while providing good driveablity and fuel efficiency.
The control module also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL) "Service Engine Soon" light on the instrument panel and store a Diagnostic Trouble Code(s) (DTC) in the control module memory. The DTC identifies the problem areas to aid the technician in performing repairs.

DESCRIPTION
General Motors Corporation uses the following control modules:
- Engine Control Module (ECM) - controls engine system and 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
The control module is an electronic computer designed to process the various input information, and send the necessary electrical response to control fuel delivery, spark control, and other emission control systems. The control module can control these devices through the use of Quad Driver Modules (QDM). When the control module is commanding a device or a component "ON," the voltage potential of the output is "LOW" or near zero volts. When the control module 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 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.

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.