Antitheft and Alarm Systems: Description and Operation

CIRCUIT OPERATION

Resistor sensing contacts are located in the Ignition Key Lock Cylinder. These contact the Key Resistor Pellet on the key when it is inserted. When the lock is rotated, battery voltage is applied through Fuse 7 to the PASS Key Decoder Module terminal A1. The Pellet resistance is then compared against the programmed value in the Module.

If the Key Pellet is the proper resistance, terminal A3 is grounded, energizing the Starter Enable Relay. At the same time, a signal is applied at terminal A2 to enable the Powertrain Module (PCM). When this signal is received by the PCM, it allows fuel injector pulses to begin.

If the Key Resistor Pellet is the wrong value, the PASS Key Decoder Module will shut down for approximately 2 to 4 minutes. During this interval there will be no output at terminals A3 or A2.

If the Ignition Switch is turned on again during this interval, the Timer will begin over again and the PASS Key Decoder Module will remain shut down for another 2 to 4 minutes. The PASS Key Decoder Module will continue this process even if a key with the correct pellet is used to turn the ignition back on. The Timer is restarted by the ignition voltage at terminal At when the Ignition Switch is turned to RUN.

Once the Timer has completed its 2 to 4 minute cycle with the ignition off, the PASS Key Decoder Module and Timer are reset. A key having the correct code can then be used to start the engine.

When the PASS Key Decoder Module senses ignition voltage at terminal A1, the Module will ground the SECURITY Indicator for approximately 2 seconds as a bulb-check function. Should the key resistance not match the programmed value in the Module, the SECURITY Indicator will remain on. If the Ignition Key circuit is open or shorted, the SECURITY Indicator will not light at all and the vehicle will not crank.

If the PCM loses the Cranking Fuel Enable signal while the engine is running, the engine will not stall, the THEFT DISABLED message (-U68) VIC will be displayed in the IPC or the VEHICLE ANTI-THEFT PROBLEM CAR MAY NOT RESTART message (+U68) VIC will be displayed on the VIC and PCM code 58 will set. If just the Cranking Fuel Enable circuit fails, the engine will restart. However, if a loss of power or ground to the PASS Key Decoder Module caused the Cranking Fuel Enable failure, the engine will not crank when attempting to restart the vehicle. Even though a car with an PCM code 58 may not restart the problem is most likely not in the Ignition Key Lock Cylinder circuit.


If the PCM does not receive a correct Cranking Fuel Enable signal when attempting to start the engine, the PCM will signal the BCM through the serial data line (800). The BCM will then command through the serial data line (800), the following message: STARTING DISABLED (-U68) VIC or VEHICLE ANTI-THEFT SYSTEM ACTIVE, REMOVE KEY FROM IGNITION, WAIT THREE MINUTES, STARTING DISABLED (+U68) VIC on the IPC or the VIC.