Grand Prix V6-3.8L VIN 2 (2004)
Body Control Module: Description and Operation
CONTENT THEFT DETERRENT (CTD) - BODY CONTROL MODULE (BCM)
The CTD system is an internal function of the Body Control Module (BCM) which utilizes class 2 serial data and various switch input information to
perform CTD functions. When the BCM detects an unauthorized entry, it activates the horns and exterior lamps. The BCM has four basic modes
(disarmed, standby, armed, and alarm) for operating the CTD system. The different modes are described below.
1. The BCM has the CTD system in a disarmed mode until the following conditions are detected:
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Ignition key turned to the OFF position.
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Any door open.
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Doors locked by either the power door lock switch or the LOCK button on the transmitter.
2. The BCM enters the standby mode when the above conditions are detected. In standby mode, the BCM commands the theft LED to flash quickly.
If all the doors are closed and the LOCK button on the transmitter is used, the BCM enters the delayed mode.
3. When the last door is closed, the BCM enters the armed mode. In armed mode, the BCM commands the theft LED to flash slowly. Any forced
entry activates the alarm mode.
4. When the BCM detects a forced entry, the BCM enters the alarm mode. The BCM activates the horns and exterior lamps for 30 seconds. This is
followed by a three minute time-out with the horn no longer active. If no new intrusions are detected after the time-out, the horn is not active. The
system must be disarmed or the intrusion condition removed after the time-out for the system to exit alarm mode.
VEHICLE THEFT DETERRENT (VTD) - BODY CONTROL MODULE (BCM)
When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the BCM supply's 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 with 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 are of the following functions:
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If the transponder value is correct, the BCM will send the fuel continue password to the PCM via the serial data circuit.
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If the transponders value is incorrect the BCM will send the fuel disable password to the PCM via the serial data circuit.
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If the BCM is unable to measure the ignition key transponder value for one second due to a damaged or missing pellet or a damaged theft
deterrent exciter module, the BCM will send the fuel disable password to the PCM via the serial data circuit.
The 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.
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 (DIG) 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.
