Principles Of Operation

Anti-Theft

Principles of Operation

Anti-Theft Indicator

NOTE: Make sure to determine if the vehicle is equipped with Passive Anti-Theft System (PATS) before following any PATS-related diagnostics. PATS is optional on this vehicle.

NOTE: Replacement of the PATS transceiver does not require the PATS keys to be programmed into the Instrument Cluster (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.

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

NOTE: If the IC or the PCM is being replaced (or both), the parameters must be reset in both modules or the vehicle experiences a PATS no-start. This occurs even if the vehicle is not equipped with PATS. Refer to Passive Anti-Theft System (PATS) Parameter Reset Passive Anti-Theft System (PATS) Parameter Reset.

The PATS 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. If the vehicle is not equipped with PATS, the anti-theft indicator does not flash with the key in the OFF position. Refer to Instrumentation and Warning Chimes Testing and Inspection for information on the anti-theft indicator.

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 can not disable a running vehicle.

A PATS no-start may involve a vehicle no-start due to either the fuel injectors not operating or the starter not operating (or both). If the PATS anti-theft indicator does not prove-out and one (or both) of the previous conditions are present, it may be due to a PATS issue. If the anti-theft indicator proves-out, and the vehicle does not start, it is probably not a PATS issue. Refer to Computers and Control Systems. If the anti-theft indicator does not illuminate at all, it may be an IC issue. GO to Symptom Chart. A low battery voltage may cause the PATS to allow starter operation, but may keep the fuel injectors from operating. Symptom Related Diagnostic Procedures

Passive Anti-Theft System (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 the data to the IC. The IC validates the code, and if it is the correct code, the IC sends 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 Service and Repair.

Passive Anti-Theft System (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 experiences a 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) Parameter Reset.

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.

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 parameter reset is necessary.
- a damaged IC.
- a damaged PCM.

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 may also be used to prove-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) 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 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 PCM need to be reset.

When the parameters in the IC are reset, it clears (erases) the PCM ID from the IC. A PCM parameter reset causes the PCM to send a PCM ID to the IC that is necessary for the system to operate. Make sure to cycle the key at least once, then turn the key ON and make an attempt to start the vehicle for 3-5 seconds before attempting more procedures. If only a PCM parameter reset occurs, the ID stored in the IC does not match the ID being sent by the PCM, and may cause a PATS-related no-start.

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 may resolve this issue. If the PCM_VFY (PCM verify status) PID reads No, and the N_KEYCODE reads 2 or more and the MASTERKEY reads Present, the IC and the PCM need to have their parameters reset. Refer to Passive Anti-Theft System (PATS) Parameter Reset Passive Anti-Theft System (PATS) Parameter Reset. In this particular scenario, the PATSENABL (vehicle enable status) PID reads Disabled.

If the PCM_VFY PID reads No, 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 Key Programming Using Diagnostic Equipment.

If the MASTERKEY PID continues to read Not Present after programming, this may indicate an inoperative 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 using Key Programming Using Two Programmed Keys Key Programming Using Two Programmed Keys. It can be toggled to DISABLE if the customer wants to disable the customer spare key programming function. Refer to Key Programming Switch State Control Key Programming Switch State Control. This switch state control does not affect the Key Programming Using Diagnostic Equipment procedure.

Also, if the unlimited key mode has been enabled, the N_KEYCODE PID always reads 2 after the first 2 keys have been programmed into the IC. If more than 2 keys are programmed, the N_KEYCODE PID always reads 2.

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 Present
- PCM_ID must read Stored
- PCM_VFY must read Yes
- PATSENABL must read Enabled