The PATS transceiver is located under the steering column shroud and communicates with the PATS ignition key. During each vehicle start sequence, the PATS transceiver reads the PATS 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.
If the IC or the PCM is being replaced (or both), the parameters must be reset in both modules or the vehicle will experience a PATS no-start. This will occur 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
in this section.
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 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 Key Programming Using Diagnostic Equipment
in this section.
PATS disables the vehicle from starting if there is:
PATS Parameter Identification (PIDs)
- 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.
- failed parameters between the IC and the PCM.
Monitoring the PATS PIDs in the IC 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 will also prove out the transceiver, circuitry and the IC. A master key is any key that is programmed into the IC (the MASTERKEY PID must display PRESNT). If the MASTERKEY PID reads NOTPREST, it may mean the key in the ignition lock cylinder is not programmed, is not a PATS key, is damaged or the transceiver, circuitry or IC may be at fault.
Viewing the MIN_KEY (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 will start.
Viewing the N_KEYCODE (number of keys programmed) PID will 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) 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, then the parameters in the PCM will 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 will send a PCM ID to the IC that is necessary for the system to operate. Make sure to make 3-5 attempts to start the vehicle for 3-5 seconds each 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, there will be no PCM ID stored in the IC, and a PATS-related no-start may occur. Carry out the IC parameter reset first, then the PCM parameter reset next. If the PCMID PID 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 PCMID PID reads STORED, the PCMVER (the PCM ID has been verified) PID will read YES.
If the PATSENABL PID reads DISABLE, and 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.
If the PATSENABL PID reads DISABLE, and 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 Key Programming Using Diagnostic Equipment
in this section.
If the MASTERKEY continues to read NOTPRESNT 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 will accept more than 2 keys (up to a maximum of 8) being programmed into the IC. Refer to Key Programming Using Two Programmed Keys
in this section. It can be toggled to DISABL if the customer does not want any more than 2 keys programmed into the IC. Refer to Key Programming Switch State Control
in this section. This switch state control does not affect the Key Programming Using Diagnostic Equipment procedure.
In summary for the IC PATS PIDs and their correct state in order for the vehicle to start:
- N_KEYCODE must read 2 or more
- MASTERKEY must read PRESNT
- PCMID must read STORED
- PATSENABL must read ENABLE
- PCMVER must read YES