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The powertrain control module (PCM) controls the fuel injector operation and the 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 theft deterrent password to the PCM. The PCM acknowledges the password and responds to the BCM that normal fuel injector and starter operation will continue. If the PCM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC 1631 will set. The engine will not start or crank as long as the condition is present. Refer to Vehicle Theft Deterrent (VTD)Circuit Description and to Vehicle Theft Deterrent (VTD) Operation in Theft Deterrent.

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 received from the VTD system. This condition can occur if an incorrect key is used when attempting to start the vehicle, or if the BCM has been replaced and the PCM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.