Theft Deterrent Control Module

NOTE: On some vehicles, if VTD system is unable to read ignition key transponder value after vehicle has started, VTD system will consider itself malfunctioning. VTD system will enter a fail enable state and will command SECURITY indicator to illuminate. When VTD system is in a fail enable state vehicle will not stall or stop running. If VTD system is in a fail enable state when ignition is switched OFF, VTD system will remain fail enable until it is able to read a learned ignition key transponder value. When VTD system is in a fail enable state VTD system is not active and vehicle will start. This feature is not available on all GM vehicle lines.

Vehicles with steering column mounted ignition switches have exciter integral to theft deterrent control module which is located within steering column. Vehicles with instrument panel mounted ignition switches have exciter modules separate from theft deterrent control module with wiring harness connecting them. Theft deterrent control module for vehicles with instrument panel mounted ignition switches is located within instrument panel. Theft deterrent control module can learn up to 10 keys (transponder values).

Theft deterrent control module uses following inputs, battery voltage, ignition switched voltage and ground circuit. Theft deterrent control module uses following outputs, password exchange with the PCM (fuel enable/disable) via class 2 serial data circuit.

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

If transponder value is correct, theft deterrent control module sends a class 2 serial data message containing module's enable password to PCM.
If transponder value is incorrect, theft deterrent control module sends a class 2 serial data message containing a disable password to PCM.
If theft deterrent control module is unable to measure ignition key transponder value for one second (due to a damaged or missing pellet or a damaged exciter), module sends class 2 serial data message containing a disable password to PCM.