The class 2 serial data circuit is used in order to communicate between the powertrain control module (PCM) and the vehicle theft deterrent (VTD) body control module (BCM) systems.
When the Passlock portion of the VTD system has sensed the proper operation of the ignition switch and lock, or determined that the switch and lock have not been tampered with, the BCM transmits a password to the PCM. Fuel delivery is enabled if this password matches the password stored in the modules 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, this DTC will set.
If a VTD failure occurs during an ignition cycle that the PCM has enabled fuel, then the BCM will enter a fail-safe mode: Fail Enable VTD System Failure with Fuel Enabled. The BCM remains in Fail Enable Mode, for the current and future ignition cycles, until the fault is corrected and a valid password 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 10-minute timer expires, and the PCM receives the correct fuel delivery password.
This diagnostic procedure supports the following DTC:
DTC P1631 Theft Deterrent Fuel Enable Signal Not Correct
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 PCM is replaced, the PCM must re-learn a valid password and crankshaft variation.
•If the BCM is replaced, the PCM 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 trying to restart.
•If a fault or tamper has been detected, the BCM will not forward the correct password to the PCM for a period of 10 minutes , even if the condition is corrected during that time period. This may cause a DTC P1631 to set in the PCM. This timer can be monitored in the Passlock Data parameter of the scan tool. Once the time has elapsed, the BCM will determine if the condition is still present.
•The PCM and BCM 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 the following for preventing the Passlock sensor from communicating with the BCM:
•Ignition switch assembly
•Passlock sensor circuitry
•Bent pins at the small Passlock sensor
•If this DTC sets along with a DTC B2960, then the problem was caused by malfunctioning Passlock components or circuitry, not the PCM.
•Inspect all related wiring and connections including the PCM 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 inspect any circuitry that is suspected of causing the intermittent complaint.
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