Principles of Operation

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.
- A minimum of 2 PATS keys must be programmed into the PCM before the vehicle will start.
- Make sure any aftermarket remote start systems have been removed from the vehicle before any PATS-related no-start concerns are investigated. If the remote start system is a Power Code(R) system, make certain it is not the cause of the no-start. Removal of the system may be necessary.
- The smart junction box (SJB) is also known as the generic electronic module (GEM).

PATS uses a visual anti-theft indicator located in the instrument cluster (IC). The 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.

Encoded 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 general procedures described that must be carried out if a new PATS key is necessary. Refer to Key Programming Using Diagnostic Equipment or Key Programming Using Two Programmed Keys. Using Diagnostic Equipment Using Two Programmed Keys

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, will ground the starter relay solenoid coil and will also allow the fuel injectors to operate. Refer to Passive Anti-Theft System (PATS) Transceiver.

PATS Operation
The PATS function is controlled by the PCM. When the ignition 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 will not ground the starter relay solenoid coil and will not allow fuel injector operation. The anti-theft indicator in the instrument cluster (IC) will flash (or may glow steadily) and the PCM will store one or more DTCs. 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. 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. 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. The PATS may cause a vehicle no start due to either the fuel injectors not operating or the starter not operating (starter relay does not close) or both. Always check for PATS DTCs from the PCM when a no-crank or no-start condition exists. A low state of charge (SOC) in the vehicle battery 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 an instrument cluster (IC) issue. GO to Symptom Chart for additional diagnostic direction. Anti-Theft - Passive Anti-Theft System (PATS)

The PATS disables the vehicle from starting if there is:
- a damaged PATS key.
- a non-programmed PATS key.
- a non-PATS key (key has no electronics).
- damaged wiring.
- a damaged transceiver.
- a damaged PCM.

PATS PIDs
Monitoring the PATS PIDs can be very useful in determining which diagnostic steps to follow. Viewing the MASTERKEY (master key) PID (with both keys) will determine if the key is a programmed key and will also prove out the transceiver, circuitry and the PCM. A master key is any key that is programmed into the PCM. Viewing the MIN_KEY (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 will determine if the minimum number of keys have been programmed into the PCM. If the N_KEYCODE PID reads 0 or 1, additional key(s) will need 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 NOTPREST, that particular key must be programmed into the PCM. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads PRESNT, that particular key is already programmed into the PCM.

The SPAREKEY (spare key) PID is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the PCM will accept more than 2 keys (up to a maximum of 8) being programmed into the PCM. 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 procedure. Refer to Key Programming Switch State Control to change the state of the SPAREKEY PID. Switch State Control

Unlimited Key Mode
This system contains a feature named unlimited key mode (UNL_KEY_ID 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 keys, but no other keys from outside can be used to operate the vehicle(s). Any randomly selected security key is acceptable. Refer to Spare Key Programming - Unlimited Key Mode. Unlimited Key Mode