Passive Anti-Theft System (PATS) - System Operation and Component Description: Pats

PATS 

The PATS function is controlled by the BCM. There are 2 main checks the PATS performs before allowing the vehicle to start. If either of these checks fail, the PATS does not allow the vehicle to start. These 2 checks are the BCM verifying that a programmed key was used to change the ignition lock cylinder to RUN or START and to verify the PCM identification to make sure it matches the PCM identification stored in memory.

When the BCM detects the ignition lock cylinder has been turned to RUN or START, it generates a challenge message. It sends the challenge message to the PATS transceiver on the transmit (TX) circuit. The transceiver in turn reads the key and generates a response message that is sent back to the BCM on the receive (RX) circuit. If the message received from the transceiver does not match a key stored in the BCM memory, the BCM prevents the vehicle from starting.

The second check is initiated by the BCM when the ignition lock cylinder transitions to RUN and powers up the PCM.

When the ignition transitions from OFF to ON and the modules initialize, the PCM sends a target challenge request to the ABS module which replies to a target challenge request to the PCM. The BCM replies and if the correct identification is received, the PATS disables and allows the vehicle to start. If the PATS prevents the vehicle from starting, a DTC sets in one of the modules.

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

The BCM controls the ignition modes and, in conjunction with the PCM and ABS, controls the PATS.