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 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 instrument cluster before the vehicle will start.
- If the instrument cluster or the powertrain control module (PCM) is being replaced (or both), the parameters must be re-set in both modules or the vehicle will experience a PATS no-start.

PATS uses a visual anti-theft indicator located in the instrument cluster. 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 for additional information on the PATS 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 instrument cluster before it can be used to start the vehicle. Up to 8 PATS keys can be programmed into the instrument cluster. If additional PATS keys are desired, a standard PATS key can be used. 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. Using Diagnostic Equipment

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 instrument cluster. The instrument cluster validates the code, and if it is the correct code, will send a message to the powertrain control module (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. Service and Repair

PATS Operation
The PATS function is controlled by the instrument cluster. When the PATS key is turned to the ON or START position, the instrument cluster 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 instrument cluster, 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 instrument cluster 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 instrument cluster 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 instrument cluster will flash (or may glow steadily) and the instrument cluster will store one or more diagnostic trouble codes (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 instrument cluster must be replaced for any reason (PATS concerns or driveability concerns), the PATS keys must also be programmed into the new instrument cluster. Refer to Key Programming Using Diagnostic Equipment. Using Diagnostic Equipment

PATS Parameter Identification (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 instrument cluster. A master key is any key that is programmed into the instrument cluster.

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 instrument cluster. There must be at least 2 keys programmed into the instrument cluster 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 instrument cluster. If the N_KEYCODE PID reads 0 or 1, additional key(s) will need to be programmed into the instrument cluster 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 instrument cluster. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads PRESNT, that particular key is already programmed into the instrument cluster.

If the instrument cluster was replaced, the parameters in the instrument cluster, then the parameters in the PCM will need to be reset. When the parameters in the instrument cluster are reset, that clears (erases) the PCM ID from the instrument cluster. A keep-alive memory (KAM) reset of the PCM (also termed a PCM parameter reset) will send a PCM ID to the instrument cluster that is necessary for the system to operate. Make sure to make 3-5 attempts to start the vehicle for 3-5 seconds each 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 instrument cluster. If only a PCM parameter reset occurs, the instrument cluster 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 instrument cluster parameter reset occurs, there will be no PCM ID stored in the instrument cluster, and a PATS-related no-start may occur. Carry out the instrument cluster parameter reset first, then the PCM parameter reset next. If the SERV_MOD reads STORED, the instrument cluster has a PCM ID stored. If it reads NOTSTRD, a KAM reset of the PCM may resolve this issue. If the PATSENABL reads NO, and the N_KEYCODE reads 2 or more and the MASTERKEY reads PRESNT, the instrument cluster, 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 instrument cluster. 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 instrument cluster will accept more than 2 keys (up to a maximum of 8) being programmed into the instrument cluster. 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 instrument cluster. 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
- SERV_MOD must read STORED
- PATSENABL must read YES

Unlimited Key Mode
PATS contains a feature called unlimited key mode and uses the PID UNL_KEY. 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 vehicles. For an individual customer, any randomly selected security key is acceptable. Refer to Spare Key Programming - Unlimited Key Mode. Unlimited Key Mode

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 instrument cluster.