GMC Repair Questions? Ask a Mechanic for Answers ASAP
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 the column connector. The Passlock(TM) sensor is an internal resistor within the ignition switch. The ignition switch receives a 5-volt reference from the body control module (BCM) via the ignition key resistor signal circuit. When in the start position, the 5-volt reference travels through the Passlock(TM) sensor within the ignition switch. This creates a unique voltage value which is returned to the BCM via the off/run/crank voltage circuit. BODY CONTROL MODULE (BCM) The body control module (BCM) contains the logic of the theft deterrent system. The BCM provides the 5-volt reference to operate the Passlock(TM) sensor. The BCM also measures the voltage of the off/run/crank voltage. 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 to a previously learned voltage code. If the voltage codes match, the BCM sends a serial data message containing a password to the engine control module (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 serial data message containing a valid password is received from the body control module (BCM), the ECM will continue to allow the fuel injectors to operate. The ECM will allow the fuel injectors to operate until it decides there is no valid password coming from the BCM. If the ECM does not receive a serial data message, or receives a serial data message with an incorrect password, the engine will crank and will not run or will start and stall immediately. SECURITY INDICATOR The instrument panel cluster (IPC) illuminates the security indicator as determined by the theft deterrent system. The security indicator is illuminated when the body control module (BCM) provides a ground on the security indicator control circuit.
FUEL LOCKOUT CYCLE When it receives a password which is incorrect or a password which indicates tamper and the engine control module (ECM) disables the fuel injectors, the fuel injectors 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: