Principles of Operation

Anti-Theft

Principles of Operation

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 experiences a Passive Anti-Theft System (PATS) no-start. This occurs 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).

NOTE: Replacement of the PATS transceiver does not require the PATS keys to be programmed into the IC again.

NOTE: 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 sure it is not the cause of the no-start. Removal of the system may be necessary.

NOTE: 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 flashes approximately 5 times after the key has been turned off. If it is not equipped with PATS, the anti-theft indicator does not flash with the key turned off.

NOTE: A minimum of 2 PATS keys must be programmed into the IC before the vehicle starts.

Anti-Theft Indicator

If the vehicle is equipped with PATS and the key is in the OFF position, the anti-theft indicator flashes every 2 seconds for 10 seconds and then turns off. With the key in the ON position, the anti-theft indicator proves-out for 3 seconds, then goes out to indicate PATS is functional and the vehicle has been enabled.

PATS uses a visual anti-theft indicator located in the IC. The anti-theft indicator proves out for 3 seconds when the ignition key is in the ON or START position under normal operation, then goes out to indicate PATS is functional and the vehicle has been enabled. If there is a PATS concern, the anti-theft 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 not equipped with PATS, the anti-theft indicator does not flash with the key in the OFF position. If the vehicle does not have PATS, the anti-theft indicator proves-out for 3 seconds, then goes out to indicate the vehicle has been enabled when the key is turned to the ON position.

Passive Anti-Theft System (PATS) Transceiver

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, sends 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 of the PATS transceiver, refer to Passive Anti-Theft System (PATS) Transceiver Service and Repair.

Passive Anti-Theft System (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 sends 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 sends 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 flashes (or may glow steadily) and the IC stores one or more DTCs. All elements of PATS must be functional before the vehicle starts. If any of the components are not working correctly, the vehicle does not start.

PATS may cause a vehicle no-start due to either the fuel injectors or the starter not operating, or both. Always check for PATS DTCs from the IC and the PCM when a no-crank or no-start condition exists. A low state of charge in the vehicle battery may cause PATS to allow the starter to crank the engine, but prevent the fuel injectors from operating. If the anti-theft indicator does not prove out (it may be either flashing or glowing steadily) and one (or both) of the previous conditions (fuel injectors and/or engine does not crank) are present, it may be due to a PATS concern. If the anti-theft indicator proves out, it may not be a PATS concern. If the anti-theft indicator does not illuminate at all, it may be an IC concern. GO to Symptom Chart. Symptom Related Diagnostic Procedures

The PATS function uses the IC and the PCM to enable or disable the engine. All elements of PATS must be functional before the engine is allowed to start. If any of the components are not working correctly, the vehicle will not start. If there is a PATS concern present, the IC sends a message to the PCM to not allow fuel injector and starter operation. If the vehicle starts and stalls, or the engine does not start at all, check the anti-theft indicator operation and if it is flashing or glowing, retrieve DTCs from the IC and the PCM and follow the PATS diagnostics.

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 does not disable a running vehicle.

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 sure 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.
- a parameter reset necessary.

Passive Anti-Theft System (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) determines if the key is a programmed key and also proves out the transceiver, circuitry and the IC. A master key is any key that is programmed into the IC.

Viewing the MIN_KEYS (minimum number of keys) PID (this PID does not change) indicates 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 starts.

Viewing the N_KEYCODE (number of keys programmed) PID determines if the minimum number of keys have been programmed into the IC. If the N_KEYCODE PID reads 0 or 1, additional key(s) 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 Not Present, that particular key must be programmed into the IC. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads Present, 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 need to be reset. When the parameters in the IC are reset, the PCM ID is cleared (erased) from the IC. A PCM parameter reset sends a PCM ID to the IC that is necessary for the system to operate.

If the PCM_ID (PCM ID status) PID reads Stored, the IC has a PCM ID stored. If it reads Not Stored, a parameter reset of the PCM resolves this concern.

If the PATSENABL (vehicle enable status) PID reads Disabled, and the N_KEYCODE PID reads 2 or more and the MASTERKEY PID reads Present, the IC and the PCM need to have their parameters reset. If the PATSENABL PID reads Disabled, and the N_KEYCODE PID reads 1 and the MASTERKEY PID reads Present, or if the N_KEYCODE PID reads 0 and the MASTERKEY PID reads Not Present, a minimum of 2 keys need to be programmed into the IC. Refer to Key Programming Using Diagnostic Equipment Using Diagnostic Equipment. If the MASTERKEY PID continues to read Not Present after programming, this may indicate a damaged key.

The SPAREKEY (spare key) PID is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the IC accepts more than 2 keys (up to a maximum of 8) being programmed into the IC. Refer to Key Programming Using Two Programmed Keys Using Two Programmed Keys. It can be toggled to DISABLE if the customer does not want any more than 2 keys programmed into the IC. Refer to Key Programming Switch State Control 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.

In summary, the PATS PIDs and their correct state in order for the vehicle to start: