Engine Control Module (ECM) Description

When the Engine Control Module (ECM) detects that the ignition is being turned ON, the ECM waits for a release message from the intelligent switching unit. If a release message is not received within a specified time, the ECM disables the engine. The engine is also disabled if the Identification (ID) code transmitted by the intelligent switching unit does not match the code stored in the ECM's memory.

Immobilization remains in effect until the ignition is turned OFF or battery power-is removed.

To prevent the vehicle from being driven, the ECM applies the following strategy:

• The ignition module is put in a bypass mode
• The ECM will not create an Electronic Spark Timing (EST) output, so no spark will be generated by the ignition coil.
• The ECM will not enable the fuel pump.
• The ECM will not enable the fuel injectors.

Serial data communication is transmitted on a single wire between the intelligent switching unit and the ECM. During diagnostic procedures or ID code changing, a scan tool is added to the communication system. An ECM with an intelligent switching unit is not exchangeable with the ECM without an immobilizer control unit.