Antitheft and Alarm Systems: Description and Operation

Anti-Theft

NOTE: The police interceptor package does not include the Passive Anti-Theft System (PATS). Make sure the vehicle is not equipped with a police interceptor package before investigating any potential PATS-related no-start issues.

PATS consists of the following components:

- Anti-theft indicator (located in the light sensor)
- Encoded ignition key(s) (the key contains a transponder)
- PATS transceiver
- PCM

PATS uses radio frequency identification technology to deter a drive-away theft. Passive means that it does not require any activity by the user.

Passive Anti-Theft System (PATS) Function

PATS function is controlled by the PCM. PATS uses the PCM to carry out all of the PATS functions such as receiving the identification code from the PATS key, controlling the starter and fuel injectors enable, and initiates the key interrogation sequence when the ignition key is turned to the ON or START position. All elements of PATS must be functional before the vehicle starts. If any of the components are not working correctly, the vehicle cannot start. If the PCM must be replaced for any reason (PATS concerns or driveability concerns), the PATS keys must be programmed into the new PCM. Refer to Key Programming Using Diagnostic Equipment Key Programming Using Diagnostic Equipment.

A PATS no-start may involve a vehicle no-start due to either the fuel injectors not operating or the starter not operating (starter relay does not close) or both. Always check for PATS DTCs from the PCM when a no-crank or no-start condition exists. A low state of charge in the vehicle battery may cause the PATS to allow starter operation, but prevent the fuel injectors from operating. If the PATS anti-theft indicator does not prove out (it may be either flashing or glowing steadily) and one (or both) of the previous conditions (fuel injectors and/or starter inoperative) are present, it may be due to a PATS issue. If the anti-theft indicator proves out, and the vehicle does not start, it is probably not a PATS issue. Refer to Computers and Control Systems for non-PATS starting information. If the anti-theft indicator does not illuminate at all, it may be a light sensor/circuitry/PCM issue. GO to Symptom Chart. Symptom Related Diagnostic Procedures

The PATS function uses the PCM to enable or disable the engine. All elements of PATS must be functional before the engine is allowed to start. If any of the components are not working correctly, the vehicle cannot start. If there is a PATS concern present, the PCM does not allow fuel injector operation and also not allow starter operation. If the vehicle starts and stalls, or the engine cannot start at all, check the anti-theft indicator operation and if it is flashing or glowing, retrieve DTCs from the PCM and follow the PATS diagnostics.

PATS is not compatible with aftermarket remote start systems, which allow the vehicle to be started from the exterior of the vehicle. These systems may reduce the security of the vehicle, and also may be the cause of no-start concerns. Remote start systems must be removed from the vehicle before any PATS-related no-start concerns are investigated.

Factory Invoiced Accessory (FIA)

Vehicles may be equipped with a dealer-installed remote start system that is a Factory Invoiced Accessory (FIA). The remote start fob for this system uses a small device that is about half the size of a conventional RKE fob, but only has one button on it. If the remote start system is installed on the vehicle and the unlimited mode is not enabled, PATS allows up to 7 PATS keys to be programmed into the PCM. The remote start system uses up one of the 8 total PATS keys that can be programmed into the PCM. The number of keys that are programmed into the PATS can be determined by viewing the PCM PID N_KEYCODE.

PATS is active only for a few seconds when the vehicle is starting. It is not a PATS concern if the vehicle stalls after it has been running for a minimum of 3 seconds. PATS does not disable a running vehicle.

PATS disables the vehicle from starting if there is:

- a damaged PATS key.
- an unprogrammed PATS key.
- a non-encoded (non- PATS) key (a conventional key or one that does not have any electronics).
- damaged wiring.
- a damaged transceiver.
- a damaged PCM.

Unlimited Key Mode

PATS contains a feature called unlimited key mode. This feature allows a customer to program more than 8 vehicle keys, if requested. Each vehicle in unlimited key mode is set up with a special, unlimited transponder security key code. This allows all the customer vehicles (or, one vehicle) to share the same mechanically cut keys (more than 8 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 Spare Key Programming - Unlimited Key Mode Spare Key Programming - Unlimited Key Mode.