Antitheft and Alarm Systems: Description and Operation

ANTI-THEFT

NOTE: If the instrument cluster (IC) or the PCM (or both) is installed, the parameters must be reset in both modules or the vehicle will experience a passive anti-theft system (PATS) no-start.

PATS consists of the following components:
- Anti-theft indicator (located in the autolamp/sunload sensor)
- Encoded (the key contains a transponder) ignition key
- PATS transceiver
- IC
- 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.

The vehicle is equipped with 2 PATS keys. A maximum of 8 PATS keys can be programmed to start the vehicle. If additional PATS keys are desired, refer to Spare Key Programming - Unlimited Key Mode. Unlimited Key Mode

PATS Function
The PATS function is controlled by the IC. The PATS uses the IC to carry out all of the PATS functions, such as receiving the identification code from the PATS key, issuing a signal to the PCM to control the starter and fuel injectors enable, and initiating the key interrogation sequence when the ignition key is turned to the ON or START position. Because of the interaction between the IC and the PCM, there are parameters that must be set if the IC or the PCM (or both) are replaced. For additional information, refer to Passive Anti-Theft System (PATS) Parameter Reset. If the IC must be replaced for any reason (PATS concerns or IC concerns), the PATS keys also must be programmed into the new IC. For additional information, refer to Key Programming Using Diagnostic Equipment. All elements of PATS must be functional before the vehicle will start. If any of the components are not working correctly, the vehicle will not start. Passive Anti-Theft System (PATS) Using Diagnostic Equipment

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 will not disable a running vehicle.

PATS may cause a vehicle no start due to either the fuel injectors or the starter not operating (starter relay does not close) or both. Always check for PATS DTCs from the IC and DTCs from the PCM when a no-crank or no-start condition exists. After a valid key read has been completed, low battery voltage may cause the PATS to allow starter operation, but prevent the fuel injectors from operating.

If the theft light 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 theft light proves out, it may not be a PATS issue. If the theft light does not illuminate at all, it may be a circuitry/IC issue. For additional information, refer to Anti-Theft, System Chart in the Diagnosis and Testing portion. Symptom Related Diagnostic Procedures

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.

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 to share the same mechanically cut keys. For an individual customer, any randomly selected security key is acceptable. For additional information, refer to Spare Key Programming - Unlimited Key Mode. Unlimited Key Mode