Engine Control Module (ECM)

Engine management and exhaust emissions are controlled by the ECM, which has the following main functions:

• Fuel injection.
• Idle speed.
• Ignition.
• Evaporative loss system.
• Engine cooling fans.
• Climate control compressor clutch demand.

The microprocessor within the ECM receives signals from various sensors and other modules and uses a pre-determined program to compute engine management functions.

Adaptive functions are incorporated in the ECM to cater for continuous adjustments to its computations to suit prevailing conditions. Because the system also controls emissions to suit all modes, neither CO levels nor idle speed require service attention or adjustment, except if an error or component failure should occur.

On Board Diagnostics are controlled by the ECM with the continuous monitoring of incoming signals and the subsequent verification against what the module expects to 'see'. Should a signal be incorrect or missing, the ECM will substitute a fixed value to provide the 'limp home mode' and alert the driver of the problem. Fixed values may be adopted for:

• Transmission oil temperature.
• Mechanical guard position.
• Throttle blade angle.
• Camshaft position.
• Intake air temperature.

Diagnostic trouble codes (DTC), including OBD II codes, are stored in the ECM memory and can be read by an appropriate retrieval tool.

Should either the ECM or TCM fail, ensure that the control housing cooling fan is operating correctly. Failure of the cooling fan MUST be rectified before renewing a control module and details of a fan failure should accompany a returned control module.

The ignition supply is the main power source for the ECM; this supply will be disconnected by an inertia switch if the vehicle is subject to a violent deceleration, as in a collision. The ECM has separate ignition and battery supply inputs. The battery input maintains the ECM memory as long as the vehicle battery is connected.