Theft Deterrent Control Module

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

Vehicles with steering column mounted ignition switches have the exciter integral with the theft deterrent control module which is located within the steering column. Vehicles with instrument panel mounted ignition switches have exciter modules separate from the theft deterrent control module with the vehicle wiring harness connecting the two. The theft deterrent control module for vehicles with instrument panel mounted ignition switches is located within the instrument panel. The theft deterrent control module can learn up to ten keys (transponder values).

The theft deterrent control module uses the following inputs, battery voltage, ignition switched voltage and ground circuit. The theft deterrent control module uses the following outputs, password exchange with the powertrain control module (PCM) via class 2 serial data circuit.

When an ignition key is inserted into the ignition lock cylinder, the transponder embedded in the head of the key is energized by the exciter coils surrounding the ignition lock cylinder. The energized transponder transmits a signal that contains its value, which is received by the theft deterrent control module. The theft deterrent control module then compares this value to a value stored in memory and performs one of the following functions:

If the transponder value is correct, the theft deterrent control module sends a class 2 message containing the modules enable password to the PCM.
If the transponder value is incorrect, the theft deterrent control module sends a class 2 message containing a disable password to the PCM.
If the theft deterrent control module is unable to measure the ignition key transponder value for one second, due to a damaged or missing pellet or a damaged exciter, it sends a class 2 message containing a disable password to the PCM.
IMPORTANT: If the PCM is unable to communicate with the theft deterrent control module (loss of class 2 state of health) after the vehicle has started, the module will consider itself malfunctioning and enter a fail enable state and illuminate the Security Indicator. The vehicle will not stall or stop running. If the PCM is in a fail enable state when the ignition is turned to OFF, it will remain fail enabled until the next time the vehicle is started. If the PCM is fail enabled the theft deterrent system is NOT active and the vehicle will start. The PCM will remain fail enabled until class 2 communication with the theft deterrent control module is restored.