Antitheft and Alarm Systems: Description and Operation

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.
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 out of over 72 million billion combinations.
Each encoded ignition key must be programmed into the PATS module before it can be used to start the engine. There are special diagnostic repair procedures that must be performed if the encoded ignition keys need to be replaced.
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 PATS 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 PATS module.
The control functions are contained in the PATS module. This module performs all of the PATS functions such as receiving the identification code from the encoded ignition key and controlling engine enable. The PATS module initiates the key interrogation sequence when the vehicle ignition switch is turned to ON or START.
PATS uses the powertrain control module (PCM) to enable or disable the engine. The PATS module communicates with the PCM over the J1850 (SCP) network in order to enable engine operation. The PATS module and the PCM use sophisticated messages in order to prevent a theft. The PATS and the PCM share security data when first installed together that makes them a matched pair. After this security data sharing, these modules will
not function in other vehicles. The PCM shared security ID is remembered even if the battery is disconnected. The PATS module also stores the vehicle's key identification code even if the battery is disconnected. There are special diagnostic repair procedures that may be performed if either the PATS module or the PCM needs replacement.
All the elements of PATS must be functional before the engine is allowed to start. If any of the components are not working properly, the vehicle will not start.
PATS uses a visual theft indicator located on the instrument cluster. This indicator will prove out for three seconds when the ignition switch is turned to ON or START under normal operation. If there is a PATS problem, the THEFT indicator will either flash rapidly or glow steadily when the ignition switch is turned to ON or START. PATS also "blips" the THEFT indicator every two seconds when the ignition is OFF to act as a visual theft deterrent. PATS also disables the starter motor in addition to the PCM disabling the engine. When PATS disables the vehicle, it will neither crank nor start. If the PATS module is removed from the vehicle, the engine will not crank. The starter relay is used as an additional means of disabling the vehicle engine. The starter relay is disabled when PATS cannot read a valid encoded ignition key at ignition ON. The PATS will not store a diagnostic trouble code (DTC) or flash the THEFT indicator it a valid encoded ignition key is read but a fault occurs in the starter relay circuit.
PATS will be activated and will disable the vehicle from starting if there is a:
- Damaged encoded key.
- Unprogrammed key.
- Non-encoded key (key has no electronics).
- Wiring concern.
- PATS transceiver concern.
- PCM concern.
- Module communications network concern.