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Anti Theft-PATS - Principles of Operation



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ANTI THEFT - PATS

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.
NOTE:Make sure any aftermarket remote start systems have been removed from the vehicle before any PATS-related no-start concerns are investigated.
NOTE:Make sure to determine if the vehicle is equipped with PATS before following any PATS-related diagnostics. PATS is optional on this vehicle.
NOTE:A minimum of 2 PATS keys must be programmed into the instrument cluster before the vehicle will start.With the key in the OFF position, the anti-theft indicator will flash every 2 seconds to indicate the PATS is functional. With the key in the ON position, the anti-theft indicator will prove-out for 3 seconds, then go out to indicate the PATS is functional and the vehicle has been enabled.
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, then it will go out to indicate the PATS is functional and the vehicle has been enabled. 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 to indicate the PATS is functional when the ignition key is in the OFF position to act as a visual theft deterrent. See Instrument Cluster.
If the vehicle does not have PATS, the anti-theft indicator will flash every 2 seconds for 10 seconds, then it will go out with the key in the OFF position. If the vehicle does not have PATS, the anti-theft indicator will prove-out for 3 seconds, then go out to indicate the vehicle has been enabled when the key is turned to the ON position.

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. There are special diagnostic procedures described in this information that must be carried out if a new PATS key is necessary. See Key Programming 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. For the removal and installation information of the PATS transceiver, see Removal and Replacement.
PATS Operation

NOTE:If the instrument cluster 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. This will occur even if the vehicle is not equipped with PATS. PATS vehicles and non-PATS vehicles have parameters in the instrument cluster and the PCM and they must be reset whenever either (or both) module(s) is (are) replaced. See Programmable Module Installation.The PATS function is controlled by the instrument cluster. With this type of PATS, there are parameters that will need to be reset if either the instrument cluster or the PCM (or both) are replaced. Refer to PATS Parameter Identification (PIDs). 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. See Key Programming 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 only a 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, and 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 PCM parameter reset will send a PCM ID to the instrument cluster that is necessary for the system to operate.
If the PCM_ID reads STORED, the instrument cluster has a PCM ID stored. If it reads NOTSTRD, a parameter reset of the PCM may resolve this issue.
If the ENABLE_S 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 ENABLE_S 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. See Key Programming 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. See 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. See Testing and Inspection. This switch state control does not affect the Key Programming Using Diagnostic Equipment, the Spare Key Programming - Unlimited Key Mode, or the Spare Key Programming - Using Diagnostic Equipment procedures.
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
- PCM_ID must read STORED
- ENABLE_S 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. See - Spare Key Programming - 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.
- a damaged PCM.
- a parameter reset necessary.
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