DTC P1631: Invalid Password Received: Description

WARNING: This page is about a different car, the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Class 2 Serial Data circuit is used in order to communicate between Powertrain Control Module (PCM) and Passlock(tm) module systems. When Passlock(tm) module has sensed the proper operation of ignition switch and lock, or determined that the switch and lock have not been tampered with, Passlock(tm) module transmits a fuel continue password to PCM. Fuel delivery is enabled if this password matches password stored in PCM memory. If a component in Passlock(tm) system has been replaced, the modules need to relearn the password of new components. If relearn procedure was not performed, this Diagnostic Trouble Code (DTC) will set. If a Passlock(tm) failure occurs during an ignition cycle that PCM has enabled fuel, then PCM will enter a fail-safe mode: Fail Enable, Passlock(tm) System Failure with Fuel Enabled. Module remains in fail enable mode, for current and future ignition cycles, until fault is corrected and a valid password is received, or until battery power is removed. If battery is disconnected or the codes are cleared, vehicle will lose its Fail Enable status and will not start until fault is corrected, the ten minute timer expires, and PCM receives the correct fuel delivery password.

When DTC P1631 sets if PCM did not receive a valid password before fuel disable decision point was reached. PCM stores DTC in history after first failure but will not illuminate the Malfunction Indicator Lamp (MIL). PCM records operating conditions at the time the diagnostic fails. PCM stores failure information in scan tools Freeze Frame/Failure Records.