The PASS-Key II® system is designed to prevent the engine from starting if the proper resistance is not sensed from the ignition key. Of the 15 key codes or resistance values available, only one will work with each BCM. Once the key code is programmed into the BCM, the resistance value is stored in a non-volatile memory.
The PASS-Key II® system prevents the engine from starting by controlling the starter relay and the PCM fuel enable input. If the PCM does not sense the proper frequency signal on the fuel enable input, fuel will not be provided to the engine.
If the wrong resistance value is sensed when the ignition switch is in the RUN position, the BCM will not ground the starter enable circuit and will not output the fuel enable signal for approximately three minutes. The engine is prevented from starting and discourages the thief from trying key codes or resistance values at random.
If the correct resistance value is sensed when the ignition switch is in the RUN position, the BCM will ground the starter enable circuit and output the fuel enable signal. The engine will start normally.
If the PASS-Key II® system detects an open or short to ground when the ignition switch is in the RUN position, the BCM will default to fail enable. Fail enable occurs when the proper key resistance is sensed before the open short to ground occurs. This has to occur for 1 minute before the fail enable is engaged. Fail enable will illuminate the security indicator lamp and allow the operator to stop and start the vehicle until the problem is corrected.
System Components
Ignition Key
The ignition key for vehicles with the PASS-Key II® system is a typical square ignition key blank and resistor. The key blank and resistor are not serviceable separately. There are 15 different resistance values. The ignition key also has mechanical cuts similar to non-PASS-Key II® ignition keys. When servicing the PASS-Key II® system, obtain all ignition keys, if possible, and verify proper values using J 35628-A .
Ignition Cylinder
The ignition cylinder contains a set of electrical contacts used to measure the resistor in the ignition key. When servicing the cylinder, be certain to maintain proper wire routing. A two pin connector at the base of the steering column connects the contacts to the vehicle wiring. The connector is also used for diagnostic purposes.
Body Control Module (BCM)
The BCM contains the logic of the PASS-Key II® system. The BCM has inputs from the battery, ignition circuits, key resistor, shock sensor, door lock, jamb, and hatch switches. The BCM has outputs to the starter, and fuel enable, security lamp circuits and also the remote hatch release. The BCM also controls power locks, interior lamps, horn chirps and parking lamps flashes for locking and arming functions.
Ignition Input
The ignition input is used to turn the BCM on. When the BCM is on, it will read the resistor and control the outputs accordingly. When the BCM is off the resistor is not read, and the starter relay and fuel enable output will not allow the engine to start. When the ignition switch is in the OFF position, the battery input to the BCM will draw about 75 milli-amps for the first ten minutes and about 2.4 milli-amps after 10 minutes of ignition off.
Key Resistor Inputs
The key resistor inputs are used to determine if the correct ignition key is being used to start the vehicle. The key resistor inputs are read when the ignition is turned on. If the key code (resistance value) of the ignition key matches the value stored in the BCM, the starter relay and fuel enable output will allow the vehicle to start.
Starter Enable Output
The starter enable circuit controls the starter relay. When the BCM sees the proper resistance at the ignition key, it grounds the starter enable circuit which allows the engine to be started. If the BCM does not sense the proper resistance at the ignition key, it will not ground the starter enable circuit.
Fuel Enable Output
The fuel enable circuit is an output from the BCM and an input to the PCM. When the BCM senses the proper resistance at the ignition key, it will output a signal to the PCM. If the BCM does not see the proper resistance at the ignition key, it will not output the signal to the PCM, the engine will start momentarily, then stall.
Security Indicator Lamp Output
The SECURITY lamp circuit is a indicator lamp output. The lamp output will be grounded during a 5 second bulb test at key on, at any time that the BCM is preventing the engine from starting, during an open or short to ground, or in the BCM is not properly programmed.
Starter Relay
The starter relay is used to stop the engine from cranking if the correct resistance is not sensed at the ignition key. It prevents the engine from cranking by opening the circuit to the starter solenoid switch.
Powertrain Control Module (PCM)
The PCM reads the fuel enable circuit to determine if fuel injection should be allowed. If the fuel enable signal is not present, the PCM will not allow fuel injection and normal engine operation.
