The vehicle theft deterrent (VTD) system functions are provided by the theft deterrent control module. The VTD system prevents vehicle operation if a valid (learned) transponder PASS-Key®III (PK3) ignition key is not used to start the vehicle. The PK3 key has a transponder embedded in the plastic head of the key. The exciter is an antenna which is made up of wire coils which surround the ignition lock cylinder. The powertrain control module (PCM) enables engine starting when it receives a valid (learned) password from the theft deterrent control module via the class 2 serial data circuit. The components of the VTD system are as follows:

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 2. 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 10 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 PCM (fuel enable/disable) 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 PCM is unable to communicate with the theft deterrent control module (loss of class 2 state of health) after the vehicle has started, the PCM will enter a fail enable state. The PCM sends a class 2 message requesting the instrument cluster to 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 VTD 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.

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

The PCM verifies that the password received from the theft deterrent control module via the Class 2 serial data circuit is correct. The PCM can learn only one enable password. If the enable password is correct, the PCM enables the starting and fuel delivery systems.

The PCM disables the starting and fuel delivery systems if any of the following conditions occur:

Important: On some vehicles, if the PCM is unable to communicate with the VTD system after the vehicle has started, the PCM will consider the VTD system to be malfunctioning. The PCM will enter a fail enable state and will command the security indicator to illuminate. When the PCM is in a fail enable state the vehicle will NOT stall or stop running. If the PCM is in a fail enable state when the ignition is switched OFF, the PCM will remain fail enable until communications with the VTD system has been restored. When the PCM is in a fail enable state the VTD system is NOT active and the vehicle will start. This feature is NOT available on all GM vehicle lines.

The ignition key for VTD equipped vehicles is a typical looking ignition key with a transponder located in the plastic end of the key. The transponder value is fixed and unable to be changed. The VTD system uses the ignition key transponder value to determine if a valid ignition key is being used to start the vehicle. There are approximately three trillion possible transponder values. There are no visible electrical contacts. The keys may be identified by the letters "PK3" stamped into the steel shank of the key. The VTD systems use the following types of ignition keys:

Master Keys

Master keys have a black plastic end for full access operation of the vehicle. Master keys may perform the following functions:

Valet Keys

Valet keys have a gray plastic end for restricted operation of the vehicle. Valet keys may perform the following functions:

The ignition lock cylinder performs all of the functions of a lock cylinder on a non VTD equipped vehicle. The ignition lock cylinder for vehicles with VTD may be located on the steering column or on the instrument panel. In either location the exciter coils surround the ignition lock cylinder such that they are very close to the head of the key which contains the transponder pellet.

The theft deterrent control module can command the instrument cluster to illuminate the SECURITY indicator only when the ignition key is in the ON position. The security indicator is a malfunction indicator and does illuminate during the bulb check when the ignition is turned to ON. If the PCM loses communication with the theft deterrent control module, the instrument cluster will also detect the loss of communication and will illuminate the SECURITY indicator. The SECURITY indicator can indicate both malfunctions (Indicator on steady) and tamper (Indicator flashing - indicating unauthorized operation). Under the following conditions the SECURITY indicator may be commanded to illuminate.

SECURITY Indicator Stays Illuminated and Engine Starts

If the theft deterrent control module was unable to measure the ignition key transponder value or the PCM lost communication with the theft deterrent control module while the engine was last running, the indicator will remain illuminated during subsequent ignition cycles. This is to remind the driver that the vehicle theft deterrent system will not be functioning until the problem is corrected. The vehicle is fail enabled and will start.

SECURITY Indicator Illuminates when Engine is Running

If the theft deterrent control module is unable to measure the ignition key transponder value or the PCM loses communication with the theft deterrent control module while the engine is running, the indicator will be illuminated. If the key is turned to OFF, the vehicle will be fail enabled and will start if the condition still exists at the next attempt to start the vehicle.

SECURITY Indicator Illuminated and Engine Does Not Start

The theft deterrent control module or the PCM has detected a problem with the theft deterrent system. The theft deterrent control module is unable to measure the ignition key transponder value. The System is in Learn Mode, refer to Programming Theft Deterrent System Components .

SECURITY Indicator Flashes and Engine Does Not Start

The theft deterrent control module has measured an incorrect transponder value when the ignition key is turned to the ON position. The transponder has not been learned by the theft deterrent control module. This is considered a tamper condition by the theft deterrent control module.