P1631

Diagnostic Chart:

Schematic:

The passlock system is designed to prevent vehicle theft by allowing the ECM to disable the fuel injectors unless a correct key (voltage) code from the passlock sensor via the mechanical key is correct. The passlock system utilizes four components: the lock cylinder, passlock sensor, Body Control Module (BCM) and Engine Control Module (ECM). When the engine is cranked, the BCM will look for a password from the passlock sensor. If the password is not received within a certain amount of time or is incorrect, the BCM will send a "fuel disable password" to the ECM over the CAN link. The SECURITY telltale will flash and the engine will not he allowed to start. If the BCM receives the correct password from the passlock sensor that it has stored in memory, it will send it over the CAN link to the ECM. If the ECM passlock password it has stored in memory does not match the BCM password; or if the ECM receives an undecided password from the BCM, it will allow the engine to start then stall within 4 seconds. The SECURITY telltale will flash for 10 minutes if the ECM receives an undecided, incorrect or fuel disable password. If the password to the ECM is correct, the engine will operate normally. The password is sent continuously by the BCM to the ECM during run mode. If the password becomes lost or incorrect during the drive cycle, the vehicle will be allowed to start on succeeding ignition cycles without the aid of passlock and the SECURITY telltale will be On steady. This mode is called fail enable mode.

DTC PARAMETERS
DTC P1631 will set if the ECM receives an incorrect or unrecognized password from the BCM.

DTC P1631 diagnostic runs continuously when engine is running or cranked.

P1631 is a (type D) DTC

DIAGNOSTIC AIDS
Diagnose any BCM passlock DTCs or communication DTCs first.

This DTC indicates the ECM received an incorrect password and may have set during the drive cycle. If the ECM detected an incorrect password during the drive cycle, the vehicle will start.

If the ECM detected an incorrect password from the BCM during an engine crank, the engine will start then stall. Perform the security system (passlock) relearn procedure.