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 will start.

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

Anti-Theft Indicator

The 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. 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 Instrument Panel, Gauges and Warning Indicators.

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 also 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 (B1138 - Memory Full) will also be flagged in the IC. The memory that is full is referring to the memory in the SJB. These additional keys (more than 4 IKTs) will start the vehicle, but will 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 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 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.

Passive Anti-Theft System (PATS) Operation

The PATS function is controlled by the IC. With this type of PATS, there are parameters that need to be reset if either the IC 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 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 Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment 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 will 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 Information. If the anti-theft indicator does not illuminate at all, it may be an IC issue. Refer to the Symptom Chart for information. A low battery voltage condition may cause the PATS to allow starter operation, but may keep the fuel injectors from operating. Symptom Related Diagnostic Procedures

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) will determine 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 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 NOTPREST, 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. Refer to Passive Anti-Theft System (PATS) Parameter Reset Passive Anti-Theft System (PATS).

When the parameters in the IC are reset, it clears (erases) the PCM ID from the IC. A PCM parameter reset will cause 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 will not match the ID being sent by the PCM, and may cause a PATS-related no-start. Carry out the IC parameter reset first, then the PCM parameter reset next, and do not cycle the key between these 2 procedures. Note that when using the Integrated Diagnostic System (IDS), the parameters in the IC and the PCM are reset at the same time.

If the PCM_ID 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 PCM_VFY PID reads NO, 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. 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 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 Integrated Keyhead Transmitter (IKT) Key Programming Using Diagnostic Equipment Using Diagnostic Equipment.

If the MASTERKEY PID continues to read NOTPRESNT after programming, this may indicate a defective key. The SPAREKEY PID is defaulted to ENABLE. With the SPAREKEY PID displaying ENABLE, the IC will accept more than 2 keys (up to a maximum of 8) being programmed into the IC using Key Programming Using Two Programmed Keys Using Two Programmed Keys. It can be toggled to DISABL if the customer wants to disable the customer spare key programming function. Refer to Key Programming Switch State Control Switch State Control. This switch state control does not affect the Key Programming 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 PRESNT
- PCM_ID must read STORED
- PCM_VFY must read YES

Unlimited Key Mode

PATS contains a feature called unlimited key mode and uses the PID UNL_KEY_ID. 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. When in the unlimited key mode, the N_KEYCODE PID will always read 2, no matter how many keys are programmed to the vehicle (after the first 2 keys have been programmed). 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.