Engine Control Module: Description and Operation

Comp. Loc:

ENGINE CONTROL MODULE

DESCRIPTION
The Engine Control Module (ECM) is a precision unit consisting of a one chip microcomputer, Analog/Digital (A/D) converter and an Input/Output (I/O) unit. It is an essential part of the electronic control system, for its functions include not only such major functions as to control the fuel injector, Idle Air Control (IAC) valve, fuel pump relay, etc., but also a self-diagnosis function and a fail-safe function as described in the following section. The ECM is installed below the instrument panel left of the steering column.

SELF-DIAGNOSIS FUNCTION
The Engine Control Module diagnoses troubles which may occur in the system when the ignition switch is in the "ON" position with the engine running. The ECM indicates a malfunction by lighting the Malfunction Indicator Lamp (MIL) when a fault occurs in any of the following systems:

^ Heated Oxygen Sensor 1 (HO2S 1).
^ Heated Oxygen Sensor 2 (HO2S 2).
^ Engine Coolant Temperature (ECT) sensor.
^ Throttle Position (TP) sensor.
^ Vehicle Speed Sensor (VSS).
^ Intake Air Temperature (IAT) sensor.
^ Mass Air Flow (MAF) sensor.
^ Camshaft Position (CMP) sensor.
^ Exhaust Gas Recirculation (EGR) system.
^ Central Processing Unit (CPU) of ECM.

OPERATION
The ECM and the MIL operate as follows:

MIL Circuit Check
The MIL lights when the ignition switch is turned to the "ON" position (engine not running), regardless of the condition of the Sequential Multiport Fuel Injection (SFI) system. This is only to check the MIL circuit.

Fault Detection
Once the engine is started and no faults are detected by the ECM, the MIL goes out. When the ECM detects a malfunction in one of the above areas, it lights the MIL to warn the driver of the occurrence of a fault.

FAIL-SAFE FUNCTION
When a malfunction occurs within the SFI system, the ECM maintains control over the fuel injector, IAC valve etc., on the basis of the calculated signals and/or backup program prestored within the ECM.

This function is called the "Fail-Safe Function." Thus, with this function, a certain level of engine performance is available even when a failure occurs, thus avoiding complete disability in engine performance.

FAIL-SAFE SYSTEMS
The systems covered are as follows:
^ Engine Coolant Temperature sensor.
^ Throttle Position sensor.
^ Mass Air Flow sensor.
^ Central Processing Unit of ECM.
^ Fuel Level Sensor.
^ Vehicle Speed Sensor.
^ Closed Throttle Position Switch.
^ Barometric Pressure Sensor.