Principles of Operation
PRINCIPLES OF OPERATIONAnti-Theft Indicator
NOTE:
- If the instrument cluster (IC) or the PCM is being replaced (or both), the parameters must be reset in both modules or the vehicle will experience a passive anti-theft system (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 IC and the PCM and they must be reset whenever either (or both) module(s) is (are) replaced. Refer to Passive Anti-Theft System (PATS) Parameter Reset. Passive Anti-Theft System (PATS)
- Replacement of the PATS transceiver does not require the PATS keys to be programmed into the IC again.
- 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.
- Make sure to determine if the vehicle is equipped with PATS before following any PATS-related diagnostics. PATS is optional on this vehicle. Check the anti-theft indicator to determine if the vehicle has PATS or not. If it is equipped with PATS, the anti-theft indicator will flash approximately 5 times after the key has been turned off. If it is not equipped with PATS, the anti-theft indicator will not flash with the key turned off. Refer to Anti-Theft Indicator Operation in the Description and Operation portion.
- A minimum of 2 PATS keys must be programmed into the IC before the vehicle will start.
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, 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 for 10 seconds and then turns off when the ignition key is in the OFF position to act as a visual theft deterrent. Refer to Instrument Panel, Gauges and Warning Indicators.
If the vehicle is equipped with PATS and the key is in the OFF position, the anti-theft indicator will flash every 2 seconds for 10 seconds and then turn off and stay off. 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.
If the vehicle is not equipped with PATS, the anti-theft indicator will not flash 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 IC 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. 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 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. For the removal and installation information of the PATS transceiver, refer to Passive Anti-Theft System (PATS) Transceiver.
PATS Operation
NOTE: 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. This will occur even if the vehicle is not equipped with PATS. PATS vehicles and non-PATS vehicles have parameters in the IC and the PCM and they must be reset whenever either (or both) module(s) is (are) replaced. Refer to Passive Anti-Theft System (PATS) Parameter Reset. Passive Anti-Theft System (PATS)
The PATS function is controlled by the IC. With this type of PATS, there are parameters that will need to be reset if either the IC or the PCM (or both) are replaced. 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 PIDs
Monitoring the PATS PIDs can be very useful in determining which diagnostic steps to follow.
Viewing the MASTERKEY (verifies if the key is programmed) 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 NOTPRESNT, 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 PCM parameter reset will send a PCM ID to the IC that is necessary for the system to operate.
If the PCMID (PCM ID status) PID reads STORED, the IC has a PCM ID stored. If it reads NOTSTRD, a parameter reset of the PCM may resolve this issue.
If the PATSENABL (vehicle enable status) PID reads DISABLED, and the N_KEYCODE PID reads 2 or more and the MASTERKEY PID reads PRESNT, the IC and the PCM will need to have their parameters reset. If the PATSENABL PID reads DISABLED, and the N_KEYCODE PID reads 1 and the MASTERKEY PID reads PRESNT, or if the N_KEYCODE PID reads 0 and the MASTERKEY PID reads NOTPRESNT, a minimum of 2 keys will need to be programmed into the IC. Refer to Key Programming Using Diagnostic Equipment. If the MASTERKEY PID continues to read NOTPRESNT after programming, this may indicate a defective key. Using Diagnostic Equipment
The SPAREKEY (spare key) PID is defaulted to ENABLED. With the SPAREKEY PID displaying ENABLED, 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 DISABLED 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, the Spare Key Programming - Unlimited Key Mode, or the Spare Key Programming - Using Diagnostic Equipment procedures. Using Two Programmed Keys Switch State Control
In summary for the PATS PIDs and their correct state in order for the vehicle to start:
Unlimited Key Mode
PATS contains a feature called unlimited key mode and uses the 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 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, terminals or connectors
- A damaged transceiver
- A damaged IC
- A damaged PCM
- A parameter reset necessary