P1631

Schematic:

The passlock system is designed to prevent vehicle theft by disabling the engine unless the passlock lock cylinder is correctly engaged by a mechanical key. The passlock system utilizes four components for theft detection: the lock cylinder, the ignition switch, the Body Control Module (BCM) and the Powertrain Control Module (PCM).

When starting the engine, the PCM looks for a password from the BCM through the class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. If an incorrect or no password received, this indicates that the engine will start and stall immediately. Security telltale will flash on the IPC for 10 minutes. If an incorrect or disable password received, (More than three invalid passwords are received) this indicates that the engine is disabled for at least 10 minutes and that the security telltale will flash for 10 minutes.

After the vehicle has passed theft detection, the PCM will continue a normal engine operation. If the PCM loses the BCM communication within the same ignition cycle, the vehicle will continue to run on the following ignition cycles. This mode is called the fail enable mode.

DTC PARAMETERS
An unrecognized or incorrect password is sent to the PCM from the BCM.

DIAGNOSTIC AIDS
Attempting to start the vehicle by substituting parts without performing the Passlock Password learn procedure may set a P1631 or P1632.
^ Diagnose any BCM Passlock or communications DTCs first.
^ Perform the Passlock Password learn procedure in the PCM replacement procedure.