The vehicle theft deterrent (VTD) 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 via the security system sensor signal circuit. The BCM then compares this value to a value stored in memory, learned key code. If the value is correct the BCM sends the fuel continue password via the serial data circuit to the powertrain control module (PCM). If the transponders value is incorrect the BCM will send the fuel disable password to the PCM via the serial data circuit. The components of the VTD system are as follows:

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 driver information center (DIC) to display the service theft - VTD fail enable message. 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.

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the body control module (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 via the security system sensor signal circuit. The BCM then compares this value to a value stored in memory, learned key code. The BCM then performs one of the following functions:

The vehicle theft deterrent (VTD) system uses the following inputs, battery voltage, ignition switched voltage, security system sensor signal and ground circuit. The VTD system uses the following outputs, security system sensor supply voltage and password exchange with the PCM, fuel continue/disable via the serial data circuit.

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the body control module (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 via the security system sensor signal circuit.

The theft deterrent exciter module uses the following inputs, security system sensor supply voltage and ground circuit. The theft deterrent exciter module uses the following outputs, security system sensor signal.

Important: On some vehicles, if the PCM is unable to communicate with the vehicle theft deterrent (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 driver information center (DIC) to display the service theft - VTD fail enable message. 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 powertrain control module (PCM) verifies that the password received from the body control module (BCM) via the serial data circuit is correct. The PCM can learn only one fuel continue password. If the fuel continue 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:

The PCM uses the following input, password exchange with the BCM, fuel continue/disable via the serial data circuit.

The ignition key for passkey III (PK3) equipped vehicles is a typical looking ignition key with a transponder located in the plastic head of the key. The transponder value is fixed and unable to be changed. The vehicle theft deterrent (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 head for full access operation of the vehicle. Master keys may perform the following functions:

Valet Keys

Important: Valet keys are NOT standard equipment on all GM vehicle lines.

Valet keys have a gray plastic head and are 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 passkey III equipped vehicle. The ignition lock cylinder for vehicles with PK3 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.

If an ignition lock cylinder is replaced, the new ignition lock cylinder must be coded to match the mechanical coding of the PK3 keys. When replacing an ignition lock cylinder, and new PK3 keys are required, the new keys must be learned by the body control module (BCM). Refer to Immobilizer System Component Programming .

Theft System Not Programmed

The body control module (BCM) or powertrain control module (PCM) will send a message to the driver information center (DIC) to display Theft System Not Programmed when either the BCM or PCM are in the vehicle theft deterrent learn mode.

Service Theft System

The PCM will send a message to the DIC to display Service Theft System when the PCM has lost communication with the BCM after the vehicle has been started. The BCM will send a message to the DIC to display Service Theft System when the BCM is unable to read the key transponder value after the vehicle has started.

Starting Disabled Due To Theft System

The BCM will send a message to the DIC to display Starting Disabled Due To Theft System when the BCM has either received no key transponder value or the incorrect key transponder value.