Passive Anti-Theft System (PATS) Operation

WARNING: This page is about a different car, the 2014 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.

The Passive Anti-Theft System (PATS) is controlled by the Body Control Module (BCM). There are 2 main checks that PATS carries out before allowing the engine to start. If either of these checks fail, PATS does not allow the engine to start and STARTING SYSTEM FAULT is displayed in the message center. These two checks are the BCM verifying the PCM ID to make sure it matches the PCM ID stored in memory and to verify that a programmed key was used to turn the ignition to the RUN or START position.

The first check is initiated by the BCM waking up the PCM by supplying voltage on the wake up control circuit. The BCM activates the wake up control circuit when:

the driver door is opened.
a remote start request is received (if equipped with factory remote start).
the brake pedal is pressed.
a key is inserted into the ignition.
or when the ignition is in the RUN or START position.

Once the PCM is awake, the BCM sends the PCM a challenge message over the High Speed Controller Area Network (HS-CAN). When the PCM receives the challenge message, it generates a response and sends it back to the BCM . If the response from the PCM does not match the response in the BCM memory, this first check fails and the engine will not start.

Once the PCM ID has been verified, PATS performs the second check to make sure a programmed key is in the ignition. When the BCM determines the ignition has been turned to the RUN or START position, 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 engine will not start.

If both the PCM ID and key verification pass, PATS is enabled and allows the engine to start. PATS cannot disable an engine that has already been started.