GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The powertrain control module (PCM) controls the fuel injector operation and the starter operation based on a vehicle theft deterrent (VTD) password from the vehicle body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed theft deterrent password to the PCM. The PCM acknowledges the password and responds to the BCM that normal fuel injector and starter operation will continue. If the PCM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC 1631 will set. The engine will not start or crank as long as the condition is present.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

    •  The PCM detects an incorrect password from the VTD system.
    •  The condition is present for less than 1 second.

Action Taken When the DTC Sets

    • The body control module (BCM) send a class to message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.
    • 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

DTC P1631 indicates that the vehicle theft deterrent password that the PCM has learned does not agree with the password received from the VTD system. This condition can occur if an incorrect key is used when attempting to start the vehicle, or if the BCM has been replaced and the PCM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.

Step

Action

Yes

No

1

Did you perform the Theft Deterrent Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent

2

Is DTC B2721, B2722, B2723 or B2735 set as a current code?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Perform the Programming Theft Deterrent System Components procedure. Refer to Programming Theft Deterrent System Components .

Did you complete the action?

Go to Step 4

--

4

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK