P1631

Circuit Description

The Vehicle Theft Deterrent (VTD) System, called a Passlock II System, is designed to prevent vehicle theft by disabling the engine unless the Passlock lock cylinder is correctly engaged by a mechanical key. The Passlock II 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 2 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:

^ No Password Received - Engine will start and stall quickly. THEFT SYSTEM telltale will flash on the Instrument Panel Cluster (IPC).
^ Incorrect or Disable Password Received (More than three invalid passwords are received) - The engine is disabled for at least 10 minutes and the THEFT SYSTEM telltale will illuminate solid on the Instrument Panel Cluster (IPC) for the 10 minutes.

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

Conditions for Setting the DTC

An unrecognized or no password is sent to the PCM from the BFC.

Action Taken When the DTC Sets

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
^ A history DTC is stored.
^ Engine fueling is disabled by the PCM.

Conditions for Clearing the MIL/DTC

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.
^ DTC(s) can be cleared by using a scan tool.

Diagnostic Aids

Attempting to start the vehicle by bypassing the Passlock II 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 P1630 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:

^ Backed out terminals or improper mating.
^ Broken locks
^ Improperly formed or damaged terminals.
^ Poor terminal to wiring connections.
^ Physical damage to the wiring harness.
^ Corrosion.

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 PCM Replacement/programming, PCM Replacement/Programming and PCM Replacement/Programming for reprogramming procedures.

Test Description

Number(s) below refer to the step number(s) 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. The scan tool can display whether or not the BFC has received and learned the password from the lock cylinder. If the password is not received, the reason the PCM set this DTC may due to a password that has not yet been learned due to a component being replaced, or a problem in the BFC or a VTD component.
3. The theft deterrent password resides in the Body Function Controller (BFC). Anytime a VTD component is replaced, the Powertrain Control Module (PCM) must learn the new BFC password. Refer to PCM Replacement/Programming portion for the password learn procedure.
4. A BFC Passlock theft deterrent DTC being set indicates that a Passlock II component may be malfunctioning. Refer to the applicable BFC table for diagnosis.
5. If no vehicle theft deterrent DTCs were set and the BFC has not learned (received) a password from the ignition lock cylinder, the BFC may need to learn the password or be malfunctioning.
6. 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 programmed and the crankshaft position system variation procedure must be performed. Refer to PCM Replacement/Programming and PCM Replacement/Programming and PCM Replacement/Programming for the Crankshaft Position Variation Procedure.
8. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.