P1631

Diagnostic Chart:

Engine Controls Schematics: Power, Ground, MIL And DLC:

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

When starting the engine, the PCM looks for a password from the BFC through the Class II serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. There are 2 modes of tamper detection:
^ No password received. The engine will start and stall quickly. The THEFT SYSTEM telltale will flash on the Instrument Panel Cluster (IPC).
^ Incorrect or disable password received (more than 3 invalid passwords received). The engine is disabled for at least 10 minutes and the THEFT SYSTEM telltale will illuminate solid on the PC for the 10 minutes.

After the vehicle has passed theft detection, the PCM will continue normal engine operation. Additional information can be found in Theft Deterrent.

CONDITIONS FOR RUNNING THE DTC
The ignition is ON.

CONDITIONS FOR SETTING THE DTC
^ An unrecognized password or no password is sent to the PCM from the BFC.
^ The condition is present for less than 1 second.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Attempting to start the vehicle by bypassing the theft deterrent system or substituting parts without performing the password learn procedure may set a DTC P1631.

If no password is received P1626 and P1630 may be set.

If the serial data loss occurred after a good theft password has been received, the PCM must be reprogrammed and the password learn and the crankshaft position variation learn procedures must be completed to allow the theft system to operate properly. Refer to PCM Replacement/Programming and CKP System Variation Learn Procedure and BCM Programming/RPO Configuration for reprogramming procedures.