Immobilizer Description and Operation: Notes

WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

The immobilizer system functions are provided by the body control module (BCM). When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the BCM supplies battery voltage to the theft deterrent exciter module. The transponder embedded in the head of the key is energized by the theft deterrent exciter module which is surrounding the ignition lock cylinder. The energized transponder transmits a signal that contains its unique value, which is received by the theft deterrent exciter module. The BCM monitors the theft deterrent exciter module for the transponder value. The BCM then compares this value to a value stored in memory, the learned key code. If the value is correct, the BCM sends the fuel enable password via serial data to the engine control module/powertrain control module (ECM/PCM). If the transponders value is incorrect the BCM will send the fuel disable password to the ECM/PCM via the serial data circuit. The components of the immobilizer system are as follows:

BCM
Theft deterrent exciter module
ECM/PCM
Ignition key (Transponder)
Security indicator