P1631

DTC P1631 Theft Deterrent Password Incorrect




Circuit Description
The Class 2 serial data circuit is used to communicate between the VCM and the Vehicle Theft Deterrent (VTD) (Passlock) Control Module Systems.

When the Passlock portion of the VTD system has sensed the proper operation of the ignition switch and lock (determined that the switch and lock have not been tampered with), the VTD system transmits a password to the VCM. The VCM enables fuel delivery if this password matches the password stored in the VCM's memory If a component in the theft deterrent system has been replaced, the modules need to relearn the password of the new components. If the relearn procedure was not performed, a DTC P1631 may set in the VCM.

If a VTD failure occurs during an ignition cycle that the VCM has enabled fuel, the VCM will enter a fail-safe mode: "Fail Enable" (VTD System Failure with Fuel Enabled). The VCM remains in "Fail Enable" mode, for the current and future ignition cycles, until the fault is corrected and a valid pass word is received, or until battery power is removed. If the battery is disconnected or the codes are cleared, the vehicle will lose its Fail Enable status and will not start until the fault is corrected, the ten minute timer expires, and the VCM receives the correct fuel delivery password.

Conditions for Running the DTC
- DTC P1626 is not active
- The VCM is not in password learn mode
- The VTD (Passlock) system is enabled.
- The fuel enable decision point has been reached (engine cranking).

Conditions for Setting the DTC
The VCM did not receive a valid password before the fuel disable decision point was reached.

Action Taken When the DTC Sets
- The vehicle does not start, or it starts then stalls.
- A DTC P1631 is stored in the VCM memory.
- The VCM will not illuminate the MIL.
- The Security lamp may be illuminated by the VTD (Passlock) system.
- The VCM disables fuel delivery until the problem is corrected and a valid password is received from the VTD (Passlock) Control Module.

Conditions for Clearing the MIL/DTC
- A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
- DTC(s) can be cleared with a scan tool.

Diagnostic Aids

IMPORTANT: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.

- If the VCM is replaced, the VCM must re-learn a valid password and Crankshaft variation.
- If the BCM is replaced, the VCM must re-learn a valid password.
- Check for published service bulletins relating to exhibited symptoms or component operation.
- If the vehicle does not start, or starts and stalls:
- Turn OFF the ignition and wait at least 5 seconds before tying to restart the engine.

- If a fault has been detected, the VTD module will not forward the correct password to the VCM for a period of ten minutes, even if the condition is corrected during that time period. This may cause a DTC P1631 to set in the VCM. This timer can be monitored in the Passlock Data parameter of the scan tool. Once the time has elapsed, the VTD module will determine if the condition is still present.
- The VCM's VTD (Passlock) parameters can be monitored with a scan tool.
- The Passlock state and the auto learn timer can be viewed in the Passlock Data Parameter of the scan tool.
- Inspect all related wiring and connections including the VCM and BCM connections. These may cause an intermittent malfunction.

An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.

Steps 1 - 4:

Important Preliminary Checks (Part 1 Of 2):

Important Preliminary Checks (Part 2 Of 2):

Test Description
Number(s) below refer to the step number(s) on the diagnostic table.
2. Some fault conditions in the VTD (Passlock) system may cause a P1631 to set in the VCM. Any VTD (Passlock) DTCs must be diagnosed prior to performing the Password Learn Procedure. A DTC B3031 may set in the VTD (Passlock) module during the Password Learn Procedure.