The Passlock theft deterrent system is designed to prevent vehicle operation if the proper key is not used to start the vehicle. The key, in normal operation, will turn the Passlock ignition lock cylinder, magnetically invoking the Passlock sensor. The Passlock sensor sends an analog voltage signal to the Body Control Module (BCM). The BCM determines if the voltage level is correct. If the BCM determines that the analog voltage level is correct, the BCM will communicate a coded password to the Powertrain Control Module (PCM) over the class II serial data link. If the PCM receives the correct coded password, it will enable the fuel injector drivers and the crank relay.

To operate properly and start the engine, the Passlock theft deterrent system requires the BCM to read the proper Passlock sensor analog voltage signal when the ignition key is rotated into the START position. This proper analog voltage signal is often referred to as the Passlock data. It is stored in the BCM and will vary from vehicle to vehicle. In the event of a failure in the reading of the Passlock sensor analog voltage, the BCM may become fail-enabled. While the engine is running, the BCM continuously monitors the Passlock sensor analog voltage for authenticity. If a failure to read authentic Passlock sensor analog voltage occurs while the engine is running, the SECURITY indicator lamp in the instrument cluster turns on, the BCM becomes fail-enabled, and the BCM may set a Diagnostic Trouble Code (DTC). The vehicle may be turned off and restarted when the BCM is fail-enabled. The SECURITY indicator will remain illuminated continuously when the BCM is fail-enabled. The vehicle will not be secured by the Passlock theft deterrent system when the BCM is fail-enabled. If a failure to read the authentic Passlock sensor analog voltage occurs before an ignition cycle (when the engine is not running), the BCM will not become fail-enabled and will not send the valid password to the PCM over the class II serial data link. The PCM will not enable the crank relay and the fuel injectors. The engine will not crank nor start and the SECURITY indicator lamp turns on.

If the BCM reads a non-authentic or tamper Passlock sensor analog voltage when the ignition key is rotated into the START position, the BCM enters a ten minute tamper mode. The SECURITY indicator flashes for the duration of the tamper mode. During this tamper mode time period, the BCM sends a fuel disable password to the PCM over the class II serial data link. The PCM disables the fuel injectors and the crank relay. The engine will not crank nor start under these conditions. The BCM remains in the tamper mode for the ten minute period even if the ignition switch is turned off.

In the even of an open or short in the class II serial data link between the BCM and the PCM, the PCM may become fail-enabled. If a failure occurs in the class II serial data link while the engine is running, the SECURITY indicator turns on, the PCM becomes fail-enabled, and the PCM may set DTCs. The vehicle may be turned off and restarted when the PCM is fail-enabled. The SECURITY indicator remains illuminated continuously when the PCM is fail-enabled. The vehicle will not be secured by the Passlock theft deterrent system under these conditions. If a failure occurs in the class II serial data link before an ignition cycle (when the engine is not running), the PCM will not receive a valid password from the BCM and the PCM will not enable the fuel injectors and the crank relay. The engine will not crank nor start and the SECURITY stays on during these conditions.

If the password is not received from the BCM to the PCM within a preset time period, the PCM will not enable the fuel injectors and the crank relay. The engine will not crank nor start and the SECURITY indicator stays on. If the BCM sends an incorrect password or a fuel disable password to the PCM, then the PCM disables the fuel injectors and the crank relay for ten minutes. Also, the SECURITY indicator turns on for ten minutes.