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 instrument cluster (IC) again.
- Make sure any aftermarket remote start systems have been removed from the vehicle before any PATS-related no-start concerns are investigated.
- A minimum of 2 PATS keys must be programmed into the IC before the vehicle will start.
- If the IC or the PCM is being replaced (or both), the parameters must be reset in both modules or the vehicle will experience a PATS no-start. Refer to Passive Anti-Theft System (PATS) Parameter Reset. Passive Anti-Theft System (PATS)
- The smart junction box (SJB) is also known as the generic electronic module (GEM).

PATS uses a visual anti-theft indicator located in the 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. Refer to Instrument Panel, Gauges and Warning Indicators on the anti-theft indicator.

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 IC before it can be used to start the vehicle. Up to 8 PATS keys can be programmed into the IC. If additional PATS keys are desired, a standard PATS key can be used. There are special general procedures described that must be carried out if a new PATS key is necessary. Refer to Key Programming Using Two Programmed Keys. 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 IC. The IC validates the code, and if it is the correct code, will send a message to the PCM to ground the starter relay solenoid coil and to also allow the fuel injectors to operate. Refer to Passive Anti-Theft System (PATS) Transceiver for removal and installation information.

PATS Operation
The PATS function is controlled by the IC. When the PATS key is turned to the ON or START position, the IC initiates the key interrogation sequence by sending a voltage signal to the PATS transceiver. The transceiver then uses its antenna to bounce a signal off the transponder in the PATS key. This process "reads" the PATS key identification code and sends the key identification code back to the IC, 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 IC will send a message to the PCM to ground the starter relay solenoid coil and to also allow the fuel injectors to operate. If it does not match one of the stored key codes, or it is only a partial key read or no key read, the IC will send a message to the PCM to not ground the starter relay solenoid coil and not allow fuel injector operation. The anti-theft indicator in the IC will flash (or may glow steadily) and the IC 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 IC must be replaced for any reason (PATS concerns or IC concerns), the PATS keys must also be programmed into the new IC. 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 in the IC and 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 IC issue. Refer to the Symptom Chart. Symptom Related Diagnostic Procedures

PATS is not compatible with aftermarket remote start systems, which allow the vehicle to be started from the exterior of the vehicle. These systems may reduce the security of the vehicle, and also may be the cause of no-start concerns. Remote start systems must be 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.

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 IC.
- 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 IC. A master key is any key that is programmed into the IC.

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 IC. There must be at least 2 keys programmed into the IC in this type of PATS before the vehicle will start.

Viewing the N_KEYCODE (number of keys programmed) PID will determine if the minimum number of keys have been programmed into the IC. If the N_KEYCODE PID reads 0 or 1, additional key(s) will need to be programmed into the IC 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 IC. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads PRESNT, that particular key is already programmed into the IC.

If the IC was replaced, the parameters in the IC, and the parameters in the PCM will need to be reset. When the parameters in the IC are reset, that clears (erases) the PCM ID from the IC. A parameter reset of the PCM will send a PCM ID to the IC that is necessary for the system to operate. After the parameter resets, make sure to make 3-5 attempts to start the vehicle for 3-5 seconds each time before attempting more procedures. The extra key cycles are necessary for the PCM ID to be sent (by the PCM) and then stored by the IC. If only a PCM parameter reset occurs, the IC may encounter 2 PCM IDs (the original one and the new one) and may cause a PATS-related no-start. If a PCM parameter reset occurs first, then the IC parameter reset occurs, there will be no PCM ID stored in the IC, and a PATS-related no-start may occur. Carry out the IC parameter reset first, then the PCM parameter reset next. Note that when using the IDS, both parameter resets will occur at the same time. If the PCMID (PCM ID status) PID reads STORED, the IC has a PCM ID stored. If it reads NOTSTRD, a KAM reset of the PCM may resolve this issue (or, use the IDS to reset the parameters in both the PCM and the IC at the same time). If the PATSENABL (vehicle enable status) PID reads NO, and the N_KEYCODE reads 2 or more and the MASTERKEY reads PRESNT, the IC, then the PCM will need to have their parameters reset.

If the PATSENABL reads NO, and the N_KEYCODE reads 1 and the MASTERKEY reads PRESNT, or if the N_KEYCODE reads 0 and the MASTERKEY reads NOTPRESNT, a minimum of 2 keys will need to be programmed into the IC. Refer to Key Programming Using Diagnostic Equipment. Using Diagnostic Equipment

If the MASTERKEY continues to read NOTPRESNT after programming, this may indicate a defective key. The SPAREKEY (spare key) PID is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the IC will accept more than 2 keys (up to a maximum of 8) being programmed into the IC. Refer to Key Programming Using Two Programmed Keys. It can be toggled to DISABL if the customer does not want any more than 2 keys programmed into the IC. Refer to Key Programming Switch State Control. This switch state control does not affect the Key Programming Using Diagnostic Equipment procedure. Using Two Programmed Keys Switch State Control

In summary for the PATS PIDs and their correct state in order for the vehicle to start:
- N_KEYCODE must read 2 or more
- MASTERKEY must read PRESNT
- PCMID must read STORED
- PCMVER must read Yes
- PATSENABL must read YES

Unlimited Key Mode
PATS contains a feature called unlimited key mode and uses the PID UNL_KEY_ID. This feature allows a customer to program more than 8 keys to their vehicle(s) if they request it. Each vehicle in unlimited key mode is set up with a special, unlimited transponder key code. This allows all the customer vehicles to share the same keys, but no other keys from the outside can be used to operate the vehicle(s). For an individual customer, any randomly selected key is acceptable. Refer to Spare Key Programming - Unlimited Key Mode. Unlimited Key Mode