Antitheft and Alarm Systems: Description and Operation

ANTI-THEFT - PASSIVE ANTI-THEFT SYSTEM (PATS)

The passive anti-theft system (PATS) uses radio frequency identification technology to deter a driveaway theft. Passive means that it does not require any action from the user to make it functional.

PATS uses a specially encoded ignition key. Each PATS key contains a permanently installed electronic device called a transponder. Each transponder contains a unique electronic identification code, with over 72 million billion combinations.

Each encoded ignition key must be programmed into the vehicle's powertrain control module (PCM) before it can be used to start the engine. There are special diagnostic repair procedures described that must be carried out if new encoded ignition keys are to be configured.

The encoded key is larger than a traditional ignition key. The key does not require batteries and should last the lifetime of the vehicle.

The PATS transceiver communicates with the encoded ignition key. The PATS transceiver is located behind the steering column shroud and contains an antenna connected to a small electronic module. During each vehicle start sequence, the PATS transceiver reads the encoded ignition key identification code and sends data to the PCM.

The control functions are contained in the PCM. The PCM carries out all of the PATS functions, such as receiving the identification code from the encoded ignition key and controlling the engine enable. The PCM initiates the key interrogation sequence when the vehicle ignition switch is turned to ON or START.

The PATS function uses the PCM and the transaxle control module (TCM) 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 will not start.

NOTE: If either the PCM or the TCM are installed, both modules require a parameter reset to allow both modules to recognize the PATS keys. Failure to carry out the parameter reset to both the PCM and the TCM may result in a no start condition.

The PATS uses a visual theft indicator located in the instrument cluster. This indicator will prove out for 3 seconds when the ignition switch is turned to ON or START under normal operation. If there is a PATS problem, this indicator either flashes rapidly or glows steadily (for more than 3 seconds) when the ignition switch is turned to ON or START. PATS also flashes the theft indicator every 2 seconds at ignition OFF to act as a visual theft deterrent.

The PATS is not compatible with aftermarket remote start systems, which allow the vehicle to be started from outside the vehicle. These systems may reduce the vehicle security level, and also may cause no-start issues. Remote start systems must be removed before investigation of PATS-related no-start issues.