The vehicle theft deterrent system is designed to prevent vehicle theft by disabling the engine unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system utilizes four components for theft detection, the lock cylinder, ignition switch, the Body Function Controller (BFC) and the Powertrain Control Module (PCM).

When starting the engine, the PCM looks for a password from the Body Function Controller (BFC) through the Class II serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. There are two modes of tamper detection:

After the vehicle has passed theft detection, the PCM will continue normal engine operation. Additional information can be found in Theft Deterrent Systems.

The Passlock II password learn procedure has been interrupted or ready to learn.

Attempting to start the vehicle by bypassing the theft deterrent system or substituting parts without performing the password learn procedure may set a DTC P1631.

If no password is received a DTC P1610, P1626 and P1631 may be set.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for the following items:

If the Body Function Controller (BFC) is replaced the PCM must be reflashed to allow the new password to be learned. Refer to Password Learn Procedure . The ignition must be turned off for at least 30 seconds then on for the PCM to learn the new BFC password.

Numbers below refer to the step numbers on the Diagnostic Table:

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This DTC is normally set and cleared during a password learn procedure. If the password learn procedure is not completed, this DTC will not be cleared.

3. The theft deterrent password resides in the Body Function controller (BFC). Anytime a VTD component has been replaced, the Powertrain Control Module (PCM) and Body Function controller (BFC) must relearn the new password. The PCM may not have finished learning the new password. Refer to the Powertrain Control Module Replacement/Programming and Crankshaft Position System Variation Learn portion of the service manual for the password learn procedure.

   If the serial data loss occurred after a good theft password has been received, the PCM must be reprogrammed and the password learn and the crankshaft position variation learn procedures must be completed to allow the theft system to operate properly. Refer to Powertrain Control Module Replacement/Programming , Crankshaft Position System Variation Learn and Password Learn Procedure for reprogramming procedures.

4. Replacement PCMs must be programmed. A reprogrammed PCM does not require the password learn procedure to be performed. The password will be learned on the first ignition cycle. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer Powertrain Control Module Replacement/Programming and Crankshaft Position System Variation Learn .

6. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.