Circuit Description

WARNING: This page is about a different car, the 2004 Pontiac Sunfire and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

The Passlock™ theft deterrent system contains a Passlock™ sensor that is part of the ignition lock cylinder assembly. The body control module (BCM) provides voltage (B+) to the Passlock™ sensor through the Passlock™ sensor power circuit when the ignition switch is in the ACCESSORY, ON, or START position. The BCM also provides a 5-volt reference to the Passlock™ data circuit. The BCM provides ground to the Passlock™ sensor through the Passlock™ sensor ground circuit. The Passlock™ sensor interfaces with the BCM through the Passlock™ sensor data circuit.

When you turn the ignition switch to the START position with the proper key, the Passlock™ sensor applies a unique resistance value to the Passlock™ Data Circuit which pulls the 5-volt reference down to a unique voltage value, which is measured by the BCM. This voltage signal is unique and varies from vehicle to vehicle. When you attempt to start the engine, the BCM compares a previously stored, learned, voltage value with the circuit voltage value.

When attempting to start the engine by means other than using the proper key in the ignition switch, the Passlock™ sensor sends a tamper signal to the BCM. The BCM compares the preset stored analog voltage value with the signal coming from the sensor. If the values do not match, the BCM sends a fuel disable password via the Class 2 serial data link to the powertrain control module (PCM). As a result, the PCM disables fuel delivery to the engine.