Principles of Operation

Anti-Theft

Principles of Operation

NOTE: Replacement of the Passive Anti-Theft System (PATS) transceiver does not require the PATS keys to be programmed into the Instrument Panel Cluster (IPC) 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: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

Anti-Theft Indicator

PATS uses a visual anti-theft indicator located in the IPC. The anti-theft indicator proves out for 3 seconds when the ignition key is in the ON or START position. 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 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 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 cannot disable a running vehicle.

A PATS no-start can involve a vehicle no-start due to either the fuel injectors 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 can be due to a PATS concern. If the anti-theft indicator proves out, and the vehicle does not start, it is probably not a PATS concern. Refer to Computers and Control Systems Information. If the anti-theft indicator does not illuminate at all, it can be an IPC concern. GO to Symptom Chart. A low battery voltage condition can cause the PATS to allow starter operation, but can keep the fuel injectors from operating. Symptom Related Diagnostic Procedures

Passive Anti-Theft System (PATS) Keys

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

PATS uses a special ignition key that is larger than a conventional ignition key. 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 IPC before it can be used to start the vehicle. A maximum of 8 PATS keys can be programmed to start the vehicle. There are special procedures described that must be carried out if a new PATS key is necessary. Refer to Key Programming Using Diagnostic Equipment Using Diagnostic Equipment or Key Programming Using Two Programmed Keys Using Two Programmed Keys.

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 data to the IPC. The IPC validates the code, and if it is the correct code, sends a message to the PCM to ground the starter relay solenoid coil and allow the fuel injectors to operate.

Passive Anti-Theft System (PATS) Operation

The PATS function is controlled by the IPC. With this type of PATS, there are parameters that need to be reset if either the IPC or the PCM (or both) are replaced. Refer to Passive Anti-Theft System (PATS) Parameter Reset Passive Anti-Theft System (PATS).

When the PATS key is turned to the ON or START position, the IPC 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 IPC, 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 IPC sends a message to the PCM to ground the starter relay solenoid coil and 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 IPC 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 IPC flashes (or may glow steadily) and the IPC 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 cannot start.

If the IPC must be replaced for any reason (PATS or IPC concerns), the PATS keys must also be programmed into the new IPC. Refer to Key Programming Using Diagnostic Equipment Using Diagnostic Equipment.

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 IPC.
- a damaged PCM.

Passive Anti-Theft System (PATS) PIDs

Monitoring the PATS PIDs in the IPC can be very useful in determining which diagnostic steps to follow. Viewing the MASTERKEY PID (verifies if the key is programmed) (with both keys) determines if the key is a programmed key and proves-out the transceiver, circuitry and the IPC. A master key is any key that is programmed into the IPC. Viewing the MIN_KEYS PID (minimum number of keys) (this PID does not change) indicates the minimum number of keys that must be programmed into the IPC in order for the vehicle to start. There must be at least 2 keys programmed into the IPC in this type of PATS before the vehicle starts. Viewing the N_KEYCODE PID (number of keys programmed) determines if the minimum number of keys has been programmed into the IPC. If the N_KEYCODE PID reads 0 or 1, additional key(s) needs to be programmed into the IPC 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 IPC. If the N_KEYCODE PID reads 1, and the MASTERKEY PID reads Present, that particular key is already programmed into the IPC. The SPAREKEY (spare key) PID is defaulted to ENABLE.

When the parameters in the IPC are reset, it clears (erases) the PCM ID from the IPC. A PCM parameter reset causes the PCM to send a PCM ID to the IPC 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 IPC does not match the ID being sent by the PCM, and can cause a PATS-related no-start. Carry out the parameter reset, and do not cycle the key until after the parameter reset selection has been highlighted, and the on-screen instructions have been followed. The IDS then resets the parameters in both the IPC and the PCM at the same time. Passive Anti-Theft System (PATS)

If the PCM_ID reads Stored, the IPC has a PCM ID stored. If it reads Not Stored, a parameter reset may resolve this issue. If the PCM_VFY PID (PCM verify) reads No, the N_KEYCODE PID reads 2 or more and the MASTERKEY PID reads Present, the IPC, and the PCM need to have their parameters reset. Refer to Passive Anti-Theft System (PATS) Parameter Reset Passive Anti-Theft System (PATS).

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

The SPAREKEY PID in the IPC is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the IPC accepts more than 2 keys (up to a maximum of 8) being programmed into the IPC using the Key Programming Using Two Programmed Keys Using Two Programmed Keys procedure. The SPAREKEY PID can be toggled to DISABLE if the customer wants to disable the customer spare key programming function. To enable or disable the spare key feature, refer to Key Programming Switch State Control Switch State Control. This switch state control does not affect the Key Programming Using Diagnostic Equipment Using Diagnostic Equipment procedure.

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

Unlimited Key Mode

PATS contains a feature named unlimited key mode that has an UNL_KEY_MODE PID (unlimited key mode). 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 mechanically cut keys, but no other keys from outside can be used to operate the vehicles. For an individual customer, any randomly selected security key that has been previously mechanically cut and electronically programmed to the vehicle is acceptable. Refer to Spare Key Programming - Unlimited Key Mode Unlimited Key Mode.