Immobilizer Description and Operation

Immobilizer Description and Operation

Circuit Description

The Passlock(TM) system is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate. The Passlock controller reads the coded Passlock(TM) data signal. The data consists of a voltage generated by a voltage divider network created between the Passlock assembly and the Passlock(TM) controller. If the data is correct, indicating rotation of the lock cylinder with the proper mechanically cut key, then the Passlock(TM) controller sends a password to the Powertrain controller over the class 2 bus to indicate that starter engagement should be allowed. The Passlock(TM) controller also interfaces with the driver displays subsystem to indicate, via a Security telltale, the Passlock(TM) subsystem's status and acute subsystem failures.

The components of the Passlock(TM) System are as follows:

* The ignition switch
* The body control module (BCM)
* The security indicator on the instrument cluster
* The engine control module (ECM)

Ignition Switch

The ignition switch contains the wiring and electrical switching portion of the column mounted ignition assembly. The ignition switch includes wiring pigtails which connect it to the base of column connector, the Passlock(TM) Sensor is an internal resistor inside the ignition switch.

Body Control Module (BCM)

The BCM contains the logic of the theft deterrent system. The BCM provides the battery positive voltage to operate the Passlock(TM) Sensor. The BCM also measures the voltage of the security sensor signal circuit. The voltage measured will indicate whether the Passlock(TM) Sensor has been activated and whether the resistance value from the sensor is a valid value or the tamper value. If voltage measured is in the valid range, the BCM compares this voltage, voltage code, to a previously learned voltage code. If the voltage codes match, the BCM sends a class 2 message containing a password to the ECM. If the voltage codes do not match, or the voltage is in the Tamper range, or there is a circuit fault, the BCM will not send the correct password to the ECM, and the vehicle will not start.

Engine Control Module

The engine control module (ECM) contains the remainder of the logic of the theft deterrent system. If a class 2 message containing a valid password is received from the BCM, the ECM will allow starter engagement. If the ECM does not receive a class 2 message, or receives a class 2 message with an incorrect password, the engine will not crank.

Theft System Indicator

The IPC illuminates the theft deterrent indicator as determined by the theft deterrent system. The IPC receives a class 2 message from the BCM requesting illumination.

* The vehicle theft deterrent (VTD) system requests the IPC to illuminate the indicator only when the ignition switch is ON.
* The content theft deterrent (CTD) system requests the IPC to illuminate the indicator only when the ignition switch is in the OFF or ACC positions or during RAP.
* The body control module performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

Fuel Lockout Cycle

When it receives a password which is incorrect or a password which indicates tamper and the ECM disables the starter, the starter remain disabled for 10 minutes even if the ignition switch is turned from the RUN position to the OFF position.

Changing the Passlock(TM) Components

The following components contain codes or passwords, or must learn codes or passwords for the Passlock(TM) system to allow the vehicle to start:

* The ignition switch
* BCM
* ECM

If any of these parts are replaced, a learn procedure must be performed. Refer to Programming Immobilizer System Components. If parts are replaced and a learn procedure is not performed, the engine will not crank.