Immobilizer System

The purpose of the immobilizer system is to prevent the vehicle from being stolen or driven by unauthorized users. Users are authorized by an electronically coded key. When the ignition is turned ON, the key is tested by the immobilizer system. While the key code is being read by the immobilizer control unit, the engine can start and run with any key that will turn the lock cylinder. The key code is read and compared with key codes that have been stored in the immobilizer control unit's memory.
If a valid key is detected, the immobilizer control unit sends a serial data release message to the powertrain control module (PCM)/engine control module (ECM). Included in the release message is an identification (ID) code which assures that neither the immobilizer control unit nor the PCM/ECM has been substituted to defeat the system.
If the PCM/ECM does not receive a release message within a specified time, or if the ID codes do not match, the PCM/ECM performs the following actions:
- Disables the fuel injector circuit.
- Disables the fuel pump circuit.
- Disables the ignition coil.
- Sets diagnostic trouble code (DTC) 53.

The above conditions are maintained until the ignition is turned OFF.

The immobilizer control unit system consists of the following components:
- Electronically coded keys.
- Detection coil.
- Immobilizer control unit.
- PCM/ECM.
- Instrument cluster indicator.
- A data link connector (DLC) to provide serial data access for a scan tool.

A PCM/ECM for a vehicle without an immobilizer control unit cannot be interchanged with a PCM/ECM that is used with an immobilizer control unit system. The immobilizer control unit and the PCM/ECM must have a matching ID code. ID coding and key coding are accomplished by using a scan tool.