Immobilizer Description and Operation
Immobilizer Description and Operation
Immobilizer - Passlock System
The Passlock system is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate or the ignition switch is operated while separated from the ignition lock cylinder case. If starting is attempted without authorization, the engine control module/powertrain control module (ECM/PCM) will disable engine starting.
The components of the Passlock system are as follows:
* Ignition lock cylinder
* Passlock sensor, part of the ignition lock cylinder case
* Body Control Module (BCM)
* Security indicator
* ECM/PCM
Passlock Sensor
The ignition lock cylinder fits inside the ignition lock cylinder case and operates the ignition switch when turned by a key with the proper mechanical cut. When the ignition key is used to turn the ignition lock cylinder to crank, a magnet on the lock cylinder passes close to the Passlock sensor within the ignition lock cylinder case. The magnet activates the security hall effect sensor which completes a circuit from the security sensor signal circuit through a resistor to the security sensor low reference circuit. The resistance value will vary from vehicle to vehicle.
If a magnet from outside of the ignition lock cylinder case is used to attempt to steal the vehicle, the tamper hall effect sensor will be activated. This completes a circuit from the security sensor signal circuit through a tamper resistor to the security sensor low reference circuit, bypassing the security resistor. If the ignition switch is forced to rotate without the correct key, or if the ignition lock cylinder is removed by force, the Passlock sensor will be damaged rendered inoperable.
Body Control Module (BCM)
The BCM contains the logic of the immobilizer system. The BCM provides the 12 volt reference to operate the Passlock sensor. The BCM also measures the voltage of the security sensor signal circuit. The voltage measured will indicate whether the Passlock sensor has been activated and whether the resistance value from the sensor is a valid value or the tamper value. If voltage is in the valid range, the BCM compares this voltage to a previously learned voltage code. If the voltage codes match, the BCM sends a serial data message containing the fuel continue password to the ECM/PCM. If the voltage codes do not match or the voltage is in the tamper range, the BCM will not send the fuel disable password to the ECM/PCM, disabling vehicle starting.
Engine Control Module/Powertrain Control Module (ECM/PCM)
The ECM/PCM contains the remainder of the logic of the immobilizer system. If a serial data message containing a valid fuel enable password is received from the BCM, the ECM/PCM will continue to allow the fuel injectors to operate. The ECM/PCM will allow the fuel injectors to operate until it decides there is no valid password coming from the BCM. If the ECM/PCM does not receive a serial data message, receives a message with an incorrect or unknown password, or receives the fuel disable message from the BCM, engine starting will be disabled.
Security Indicator
The instrument panel cluster (IPC) illuminates the security indicator as determined by the immobilizer system. The IPC receives a serial data message from the BCM requesting illumination.
* The immobilizer 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 position.
* The BCM performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
Fuel Lockout Cycle
When the ECM/PCM receives a password which is incorrect or a password which indicates tamper and starting is disable, the immobilizer system will disable engine starting for an additional 10 minutes, even if the ignition switch is turned from the RUN position to the OFF position.