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 is applied through the VATS IGN 1 Fuse 5 to the PASS Key Decoder Module. The Pellet resistance is then compared with 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 Engine Control Module (ECM). When this signal is received by the Engine Control Module (ECM), 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 3 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 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 A1 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.

If there is a failure involving the wire from terminal A2 of the PASS Key Decoder Module to the ECM, or a loss of power or ground to the PASS Key Decoder Module, a message will be displayed on the CCDIC.

If the ECM does not receive the Cranking Fuel Enable signal, the "Starting Disabled..." message will be scrolled on the CCDIC.

If this message is displayed, the key should be removed from the Ignition. The PASS Key Decoder Module will shut down for 2 to 4 minutes and the vehicle will not start during this time period. If the Ignition Switch is turned ON during this time period, the Timer will reset and the PASS Key Decoder Module will remain shut down for another 2 to 4 minutes.

If the ECM loses the Cranking Fuel Enable while the engine is running, the engine will not stall. If this occurs, the "Theft System Problem..." message will be displayed on the CCDIC and Code 58 will be set. Once the engine is shut off with this message displayed, it is likely that the engine will not start again. This message will also appear on the CCDIC if there is a loss of power or ground to the PASS Key Decoder Module.