The PCM controls fuel injector and starter operation based on a vehicle theft deterrent (VTD) password from the vehicle body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed VTD password to the PCM. The PCM acknowledges the password and responds to the BCM so that normal fuel injector and starter operation will continue. If the PCM detects an incorrect password (VTD system failure or attempted vehicle theft), the engine will not start or crank as long as the condition is present and DTC P1631 will set.

The ignition is ON.

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

DTC P1631 indicates that the vehicle theft deterrent password that the PCM has learned does not agree with the password being received from the VTD system. This condition can occur if an incorrect key is being used when attempting to start the vehicle or if the BCM has been replaced and the PCM's password learn function has not been enabled. If the BCM has been replaced, the password must be relearned. Refer to Theft Deterrent System.

Refer to Programming Replacement Lock Cylinder, Body Control Module or Powertrain Control Module for VTD system service procedures.

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.