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Anti-Theft




Anti-Theft

Principles of Operation

Passive Anti-Theft System (PATS) Operation

The Passive Anti-Theft System (PATS) is controlled by the Body Control Module (BCM). There are 2 main checks that PATS (Passive Anti-Theft System) carries out before allowing the engine to start. If either of these checks fail, PATS (Passive Anti-Theft System) does not allow the engine to start and STARTING SYSTEM FAULT is displayed in the message center. These two checks are the BCM (Body Control Module) 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 (Body Control Module) waking up the PCM by supplying voltage on the wake up control circuit. The BCM (Body Control Module) 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 (Body Control Module) 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 (Body Control Module). If the response from the PCM does not match the response in the BCM (Body Control Module) memory, this first check fails and the engine will not start.

Once the PCM ID has been verified, PATS (Passive Anti-Theft System) performs the second check to make sure a programmed key is in the ignition. When the BCM (Body Control Module) 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 (Passive Anti-Theft System) 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 (Body Control Module) on the receive (RX) circuit. If the message received from the transceiver does not match a key stored in the BCM (Body Control Module) memory, the engine will not start.

If both the PCM ID and key verification pass, PATS (Passive Anti-Theft System) is enabled and allows the engine to start. PATS (Passive Anti-Theft System) cannot disable an engine that has already been started.

Spare Key Programming

The customer spare key programming allows spare keys to be programmed (up to a maximum of 8) to the BCM (Body Control Module) without having to use a scan tool. Two programmed keys are required to carry out the procedure. This procedure can be disabled so that spare keys can only be programmed to the vehicle using a scan tool. Refer to Key Programming - Program a Key Using Two Programmed Keys for the customer spare key programming procedure or Key Programming - Enable/Disable Spare Key Programming for the enable/disable procedure.

Unlimited Key Mode

Passive Anti-Theft System (PATS) contains a feature called unlimited key mode. This feature allows a customer to program more than 8 keys to their vehicle if they request it. Each vehicle in unlimited key mode is set up with a special unlimited transponder security key code. This allows all of the customer vehicles to share the same mechanically cut keys. For an individual customer, any randomly selected security key that has been previously mechanically cut and electronically programmed to the vehicle is acceptable. Refer to Key Programming - Unlimited Key Mode .

Passive Anti-Theft System (PATS) PIDs

The PATS (Passive Anti-Theft System) PIDs are a useful tool when diagnosing a PATS (Passive Anti-Theft System) concerns. They can also be used to determine if unlimited key mode or customer spare key programming are enabled/disabled.





Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor that when used with module software can be used to monitor and control current flow on module outputs. The FET (Field-Effect Transistor) protection strategy is used to prevent module damage in the event of excessive current flow.

The BCM (Body Control Module) utilizes an FET (Field-Effect Transistor) protective circuit strategy for many of its outputs (for example, a headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET (Field-Effect Transistor) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET (Field-Effect Transistor) protection) and the circuit is still shorted, the FET (Field-Effect Transistor) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each FET (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the continuous DTCs. The module does not allow this code to be cleared or the circuit restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These DTCs can be cleared using the module on-demand self-test, then the Clear DTC operation on the scan tool (if the on-demand test shows the fault corrected). The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTCs U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and the module must be replaced after the repair.

The BCM (Body Control Module) FET (Field-Effect Transistor) protected output circuit for PATS (Passive Anti-Theft System) is the wake up control output.
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