Engine Control Module: Description and Operation

The engine controller used on this vehicle is referred to as a Single Module Engine Controller (SMEC). This controller regulates the following:

- Ignition Timing
- Air/Fuel Ratio
- Emission Control Devices
- Cooling Fan
- Idle Speed
- Alternator charging rate

The SMEC receives a variety of input signals from different switches and sensors. From these inputs, the SMEC determines the injector pulse width, ignition coil dwell, idle speed, purge, alternator charging rate, and cooling fan operation.

The Automatic ShutDown (ASD) Relay is not located inside the SMEC, but it is turned OFF and ON by the SMEC. Distributor signals go directly to the SMEC, and in the event that the SMEC sees no signal, no power is allowed to flow to the ASD relay. If no power gets to the ASD relay, then the ASD relay acts as an open switch in the power circuits to the fuel pump and ignition coil, causing a no start condition.

The SMEC constantly tests many of its input and output circuits to verify that all of the circuits are operating within their parameters. If a fault is found in one of its major systems, it is stored in its memory. Information concerning any faults that are stored can be displayed to the technician using an appropriate scan tool or the instrument panel's CHECK ENGINE lamp. For more information concerning on-board diagnosis and extracting fault codes refer to Powertrain Management/Computers and Control Systems/Testing and Inspection/Procedures.

The SMEC contains a voltage converter used to convert battery voltage to regulated outputs of 5.0 and 8.0 volts. The 5.0 volt output is used as a reference voltage for the Throttle Position Sensor (TPS) and the Manifold Absolute Pressure (MAP) Sensor. The 5.0 volt output is also used by the logic circuits. The 8.0 volt output is used by the distributor pick-up.