Anti-Theft System Operation

The passive antitheft system components function as follows:

THEFT indicator
- The passive anti-theft system utilizes the same (THEFT) indicator, (located in the instrument cluster) that the anti-theft alarm system (if equipped) uses.
- The indicator provides system proveout and operating status to the customer or service technician.
- The active anti-theft alarm system uses the theft indicator when the ignition switch is turned OFF.
- When the ignition switch is turned to RUN/START the passive anti-theft system will activate the THEFT indicator signal ON for two seconds, then OFF to indicate Key Code Received/Vehicle Enabled (programmed key).

Any other THEFT indicator illumination indicates a Passive Anti-theft System (PATS) concern:

- THEFT indicator ON two seconds, then OFF one second, then ON continuously indicates key code received/vehicle disabled (Assembly plant use only, less than two keys programmed).
- THEFT indicator ON two seconds, then flash for one minute, then flash Fault Code 16 ten times indicates key code received I vehicle enabled or disabled, no Powertrain Control Module (PCM) verification.

- If vehicle starts, PCM is not working with PATS control module.
- If vehicle does not start, the J 1850 Communication Network may need service.

- THEFT indicator flashes for one minute indicates no key code received. Causes include:

- damaged key
- non-encoded key
- wiring concern
- PATS module

- THEFT indicator flashes for 15 minutes indicates key code received/vehicle disabled (key not programmed).

Encoded Ignition Key
- When the vehicle ignition switch is placed into either RUN or START the control module initiates a key interrogation sequence.
- The PATS control module starts an interrogation period by supplying both power and the carrier signal to the transceiver to energize the ignition key.
- After the energize period has expired, the key transmits its ID code to the transceiver module.
- This ignition key is much larger in size due to the electronics that are located in the head of the ignition key.

Transceiver
- The transceiver module is used to interface the PATS control module to the encoded ignition key.
- Sends power to the encoded key and receives the ignition key data signal.
- In turn, the transceiver sends the key code to the PATS control module which determines if the key being used is a properly coded key.

Passive Anti-Theft System Module
- The control module contains circuitry to interface to the vehicle electrical system, the transceiver module, the vehicle J1850 communications network and the THEFT indicator located in the instrument cluster.
- The control module uses a microprocessor to control the system functions.
- The control module microprocessor stores the ignition key codes in Non-volatile Random Access Memory (NVRAM).
- The control module can be diagnosed through the data link connector.

Powertrain Control Module (PCM)
- The passive anti-theft system utilizes the engine management capabilities of the PCM to enable or disable the engine.
- The J1850 communications network is used to send and receive messages to and from the PCM.
- At each engine start sequence, the PCM allows fuel and spark until the engine is running.
- Within one second after engine start, the PCM must receive an enable signal from the anti-theft system control module or the engine is dis abled.
- If the passive anti-theft system control module recognizes a stored ignition key code and there is no J1850 communications network concern preventing the PCM recognizing the start enable signal from the passive anti-theft system module, the engine will start and run.

Vehicle Disabling

The passive anti-theft system will be activated and will disable the vehicle from starting if any of the following conditions exist:
- damaged encoded key
- unprogrammed key
- non-encoded key (key has no electronics)
- wiring concern
- transceiver concern
- passive anti-theft control module concern
- J 1850 Communications-Network concern
- PCM concern

Vehicle Enabling

For normal anti-theft system proveout and engine enabling to occur, the THEFT indicator must proveout as follows:
- Normal operating proveout on theft indicator is two seconds ON then OFF after the ignition switch has been turned from OFF to RUN/START position. This vehicle should start.
- If normal two-second proveout occurs and engine cranks for more than one second after ignition switch is turned to START position but fails to start, the concern is not in the passive anti-theft system.