Principles Of Operation

Anti-Theft

Principles of Operation

Anti-Theft Indicator

NOTE: Replacement of the Passive Anti-Theft System (PATS) transceiver does not require the PATS keys to be programmed into the PCM again.

NOTE: Make sure any aftermarket remote start systems have been removed from the vehicle before any PATS-related no-start concerns are investigated.

PATS uses a visual anti-theft indicator located in the light sensor. The anti-theft indicator proves out for 3 seconds when the ignition key is in the ON or START position under normal operation. If there is a PATS concern, this indicator either flashes rapidly or glows steadily when the ignition key is turned to the ON or START position. PATS also flashes the anti-theft indicator every 2 seconds when the ignition key is in the OFF position to act as a visual theft deterrent. For the anti-theft indicator/light sensor removal procedure, refer to Exterior Lighting Service and Repair.

Encoded Passive Anti-Theft System (PATS) Keys

PATS uses a special ignition key that is larger than a conventional ignition key because it contains a permanently-installed electronic device called a transponder. Each transponder contains a unique encrypted identification code which is one of a very large number of combinations. The addition of this transponder to the key makes it an "encoded" key. The PATS key does not require batteries and should last the lifetime of the vehicle. Each PATS key must be programmed into the PCM before it can be used to start the vehicle. There are special diagnostic procedures described that must be carried out if a new PATS key is necessary. Refer to Key Programming Using Diagnostic Equipment Key Programming Using Diagnostic Equipment.

Passive Anti-Theft System (PATS) Transceiver

The PATS transceiver is located under the steering column shroud and communicates with the encoded ignition key. During each vehicle start sequence, the PATS transceiver reads the encoded ignition key identification code and sends data to the PCM. The PCM validates the code, and if it is the correct code, grounds the starter relay solenoid coil and allows the fuel injectors to operate.

Passive Anti-Theft System (PATS) Operation

The PATS function is controlled by the PCM. When the PATS key is turned to the ON or START position, the PCM initiates the key interrogation sequence by sending a voltage signal to the PATS transceiver. The transceiver then uses its antenna to communicate with the transponder in the PATS key. This process "reads" the PATS key identification code and sends the key identification code back to the PCM, which interprets it and determines if it matches one of the stored key codes. If it does match one of the stored key codes, the PCM grounds the starter relay solenoid coil and allows fuel injector operation. If it does not match one of the stored key codes, or it is only a partial key read or no key read, the PCM cannot ground the starter relay solenoid coil and does not allow fuel injector operation. The anti-theft indicator in the light sensor flashes (or may glow steadily) and the PCM will store one or more DTCs. 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.

The PATS disables the vehicle from starting if there is:

- a damaged PATS key.
- a non-programmed PATS key.
- a non- PATS key (a conventional key or one that has no electronics).
- damaged wiring.
- a damaged transceiver.
- a damaged PCM.

Passive Anti-Theft System (PATS) PIDs

Monitoring the PATS PIDs can be very useful in determining which diagnostic steps to follow. Viewing the MASTERKEY PID (verifies the key is programmed) (with both keys) determines if the key is a programmed key and proves-out the transceiver, circuitry and the PCM. A master key is any key that is programmed into the PCM. Viewing the MIN_KEYS (minimum number of keys) PID (this PID does not change) determines the minimum number of keys that must be programmed into the PCM. There must be at least 2 keys programmed into the PCM in this system. Viewing the N_KEYCODE (number of keys programmed) PID determines if the minimum number of keys have been programmed into the PCM. If the N_KEYCODE PID reads 0 or 1, additional key(s) needs to be programmed into the PCM in order to meet the minimum of 2 keys. If the N_KEYCODE PID reads 0 or 1, and the MASTERKEY PID reads Not Present, that particular key must be programmed into the PCM. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads Present, that particular key is already programmed into the PCM. The SPAREKEY PID is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the Key Programming Using Two Programmed Keys procedure can be used. It can be toggled to DISABLE if the customer does not want any more than 2 keys programmed into the PCM using the Key Programming Using Two Programmed Keys Key Programming Using Two Programmed Keys procedure. Refer to Key Programming Switch State Control Key Programming Switch State Control.

Unlimited Key Mode

This system contains a feature called unlimited key mode (UNL_KEY_MODE PID). This feature allows a customer to program more than 8 keys to their vehicle if they request it. 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, but no other keys from outside can be used to operate the vehicle(s). 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.