PASS-Key® II Vehicle Theft Deterrent (VTD) allows the vehicle to start only when the resistance pellet of the ignition key is recognized by the body control module  (BCM). If an incorrect resistance value is seen by the BCM, the engine is prevented from starting in two ways:

On vehicles equipped with VTD, the BCM will initiate an audible alarm cycle if an attempt is made to start the vehicle with an incorrect ignition key.

Voltage is applied to the BCM through circuit 39 when the ignition key is inserted into the ignition lock cylinder and turned to the START position. The BCM checks the pellet resistance of the ignition key through circuit 1073, through circuit 1074, and the ignition key lock cylinder. If the resistance is correct, the BCM applies ground through circuit 625 to the starter relay coil. At the same time, the BCM applies a fuel enable signal through circuit 229 to the powertrain control module (PCM). The PCM allows the vehicle to start and run and then tests circuit 229. If the fuel enable signal is present from the BCM, the engine continues to run. If the signal is not present, the PCM disables the fuel injectors, and the engine stops.

If the resistor pellet has the wrong resistance value, the BCM disables vehicle starting for approximately 3 minutes. The starter relay and the fuel injectors are disabled. After the 3 minute period the vehicle can be started with the correct ignition key.

The BCM grounds the instrument cluster circuit 728 to illuminate the security indicator. The following describes the conditions and the modes of indicator illumination:

1. When the ignition switch is turned to the RUN position or the START position, the indicator illuminates for a 5 second bulb test.
2. When an attempt is made to start the vehicle with an incorrect ignition key, the indicator is illuminated for approximately 3 minutes. The vehicle is disabled, and the indicator remains illuminated for the entire 3 minute period, regardless of the position of the ignition switch.
3. Under any of the following conditions the indicator will flash at a rate of once per second and the vehicle will not start:

•	The resistor sensing contacts of the ignition switch are open

•	Circuit 1073 or circuit 1074 is open or shorted

4. If the ignition key resistor pellet reads infinite (open), the vehicle is disabled and the indicator flashes once per second. The vehicle will start immediately if a good key is used.
5. When an unprogrammed BCM is installed, the vehicle will start but the indicator will flash at a rate of once per second under these conditions:

•	The resistor sensing contacts of the ignition switch are open

•	Circuit 1073 or circuit 1074 is open or shorted

•	The ignition key resistor pellet reads infinite (open)

6. Circuit 1073 and circuit 1074 are continuously monitored by the BCM. The indicator illuminates if a fault is detected in either circuit 1073 or circuit 1074 for one minute. If the fault goes away after one minute, the indicator turns off and the system functions normally.
7. If any of the above faults occur while the engine is running or when the ignition switch is turned to the off position, the indicator turns on. The VTD system is disabled, and the BCM allows the vehicle to start in the Fault Enable mode. The indicator will remain on whenever the ignition switch is in the RUN position until the fault is corrected. The indicator remains illuminated for approximately one minute after the fault is corrected.