System Operation: Pats: Notes

The PATS function is controlled by the BCM and the PCM. There are 2 main checks the PATS carries out before allowing the vehicle to start. These 2 checks are:

• The BCM verifying a programmed key when it is inserted into the ignition lock cylinder.
• The PCM verifying the BCM identification to make sure it matches the identification stored in memory when the ignition state changes to RUN or START.

If either of these checks fail, the PATS does not allow the vehicle to start.

When the BCM detects a key inserted into the ignition lock cylinder, it generates a challenge message. It sends the challenge message to the PATS transceiver over a LIN-based circuit. The transceiver reads the key and generates a response message to the BCM. If the message received from the PATS transceiver does not match a key stored in the BCM memory, the BCM does not respond to the PCM challenge request when the ignition transitions out of off.

The BCM activates the wake-up control circuit when a key is inserted into the ignition lock cylinder or a remote start request is received (if equipped with factory remote start).

The BCM wakes up the PCM by supplying voltage on the wake-up control circuit.

Once the PCM is awake, the PCM sends the BCM a challenge message over the HS-CAN. When the BCM receives the challenge message, it generates a response and sends it back to the PCM. If the response from the BCM does not match the data in the PCM memory, this check fails and the vehicle does not start.

If the PCM identification and key verification checks pass, the PATS allows the vehicle to start. The PATS cannot disable or stall a vehicle that is already running.

PATS Parameter Identifications (PIDs) 

In conjunction with Diagnostic Trouble Codes (DTCs), the PATS Parameter Identifications (PIDs) are a useful tool when diagnosing PATS concerns.