Antitheft and Alarm Systems: Description and Operation

ANTI-THEFT

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

The PATS uses a specially encoded ignition key. Each encoded ignition 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 powertrain control module (PCM) before it can be used to start the engine. There are special diagnostic 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 life of the vehicle.

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

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

The PATS function uses the PCM to enable or disable the engine. All elements of the 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.

The PATS uses a visual anti-theft indicator located on top of the instrument panel. This indicator proves out for 3 seconds when the ignition switch is in the ON or START position 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 in the ON or START position. PATS also flashes the anti-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.