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 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: 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 IC. The 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. Refer to Instrumentation, Message Center, and Warning Chimes [1][2]Description and Operation for information on the anti-theft indicator.

Encoded Passive Anti-Theft System (PATS) Keys

PATS uses a special ignition key, called an Integrated Keyhead Transmitter (IKT) key that is larger than a conventional ignition key. It contains a permanently installed electronic device called a transponder and also has the Remote Keyless Entry (RKE) transmitter integrated into the keyhead. 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. The transmitter portion of the IKT key has a battery. Each PATS key must be programmed into the IC before it can be used to start the vehicle. A maximum of 4 IKT keys can be programmed to start the vehicle and also operate the RKE functions. If more than 4 IKT keys are programmed, the RKE portion of the additional IKT keys does not operate and the SJB sets a memory full DTC (B1138 - Memory Full). The same DTC id also flagged in the IC. The memory that is full is referring to the memory in the SJB. These additional keys (more than 4 IKTs) starts the vehicle, but does not operate the RKE system. If additional PATS keys are desired, a standard PATS key (a non-IKT key) can be used. There are special diagnostic procedures described that must be carried out if a new PATS key is necessary. Refer to Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment or Key Programming Using Two Programmed Keys Key Programming Using Two Programmed Keys.

Factory Invoiced Accessory (FIA) Remote Starter

Vehicles may be equipped with a dealer-installed factory-invoiced remote start system that is a Factory Invoiced Accessory (FIA). The remote start fob for this system uses a small device that is about half the size of a conventional RKE fob, but only has one button on it. If the remote start system is installed on the vehicle and the unlimited mode is not enabled, the PATS allows up to 7 PATS keys to be programmed into the Instrument Cluster (IC). The remote start system uses up 1 of the 8 total PATS keys that can be programmed into the IC. The number of keys that are programmed into the PATS can be determined by viewing the IC PID N_KEYCODE.

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 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 allow the fuel injectors to operate.

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 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. 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 Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment.

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.

The PATS may cause a vehicle no start due to either the fuel injectors not operating or the starter not operating (starter relay does not close) or both. Always check for PATS DTCs in 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 the PATS to allow starter operation, 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 starter inoperative) 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. Anti-Theft

PATS is not compatible with aftermarket remote start systems, which allow the vehicle to be started from the exterior of the vehicle. These systems may reduce the security of the vehicle, and may also be the cause of no-start concerns. 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 certain 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.

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) 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 parameters in the PCM need to be reset. When the parameters in the IC are reset, that clears (erases) the PCM ID from the IC. A parameter reset of the PCM sends a PCM ID to the IC that is necessary for the system to operate. After the parameter resets, make sure to make 3-5 attempts to start the vehicle for 3-5 seconds each time before attempting more procedures. The extra key cycles are necessary for the PCM ID to be sent (by the PCM) and then stored by the IC. If only a PCM parameter reset occurs, the IC may encounter 2 PCM IDs (the original one and the new one) and may cause a PATS-related no-start. If a PCM parameter reset occurs first, then the IC parameter reset occurs, no PCM IDs store in the IC, and a PATS-related no-start may occur. Note that when using the Integrated Diagnostic System (IDS), both parameter resets occur at the same time. If the PCM_ID (PCM ID status) PID reads Stored, the IC has a PCM ID stored. If it reads Not Stored, a Keep Alive Memory (KAM) reset of the PCM may resolve this concern (or, use the IDS to reset the parameters in both the PCM and the IC at the same time). If the PATSENABL (vehicle enable status) PID reads Enabled, and the N_KEYCODE reads 2 or more and the MASTERKEY reads Present, the IC and the PCM need to have their parameters reset.

If the PATSENABL reads Disabled, and the N_KEYCODE reads 1 and the MASTERKEY reads Present, or if the N_KEYCODE reads 0 and the MASTERKEY reads Not Present, a minimum of 2 keys need to be programmed into the IC. Refer to Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment.

If the MASTERKEY continues to read Not Present after programming, this may indicate a defective 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 Key Programming 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 Key Programming Switch State Control. This switch state control does not affect the Key Programming Using Diagnostic Equipment procedure.

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

- 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

Unlimited Key Mode

PATS contains a feature called unlimited key mode and uses the PID UNL_KEY_MODE. This feature allows a customer to program more than 8 keys to their vehicle(s) if they request it. Each vehicle in unlimited key mode is set up with a special, unlimited transponder key code. This allows all the customer vehicles to share the same mechanically cut keys, but no other keys from the outside can be used to operate the vehicle(s). For an individual customer, any randomly selected key that has been previously mechanically cut and electronically programmed to the vehicle is acceptable. Refer to Spare Key Programming - Unlimited Key Mode Spare Key Programming - Unlimited Key Mode.