GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon XL - 4WD 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 DTC B3031

Circuit Description

The Passlock™ system is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate or the ignition switch is operated while separated from the ignition lock cylinder case. The body control module (BCM) provides security system sensor power and low reference for the Passlock™ sensor. The BCM also measures the security system sensor voltage.

When the correct key is used to start the vehicle, a magnet on the lock cylinder passes close to the Passlock™ sensor within the ignition lock cylinder case. The magnet activates the security hall effect sensor in the Passlock™ sensor which completes a circuit from the security sensor signal circuit through a resistor to the security sensor low reference circuit. The resistance value will vary from vehicle to vehicle. The BCM will measure the voltage on the security sensor signal circuit and compare this voltage to a previously learned voltage. If the voltage measured is within the valid range, the BCM will send a class 2 message to the powertrain control module (PCM) to enable vehicle starting. If the voltage measured is not within the valid range, a class 2 message will be sent to the PCM to disable starting of the vehicle.

Conditions for Setting the DTC
    • A new BCM has been installed and the ignition is turned to the ON position but not rotated to the CRANK position. Once the ignition switch has been rotated to the CRANK position, the BCM will learn the Passlock™ code. The theft relearn procedure will need to be run in order to make the powertrain/vehicle control module (PCM/VCM) receive the correct fuel enable password.
    • The BCM is in the learn mode but does not see a valid Passlock™ sensor code because of a sensor or a wiring problem.

Action Taken When the DTC Sets

The vehicle will not run. The security indicator will be ON.

Conditions for Clearing the MIL/DTC
    • The DTC will clear after an ignition cycle has occurred after the BCM has learned a valid code.
    • Using a scan tool.

Diagnostic Aids
    • Prior to replacing a BCM, ensure that all of the diagnostics have been completed. Refer to Diagnostic Trouble Code (DTC) List .
    • Inspect the Passlock™ sensor harness for intermittent or poor connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Tests for the proper operation of the 12-volt reference Security Sensor Power circuit, sensor ground circuit, and Passlock™ sensor signal (data) circuit. Troubleshoot the appropriate DTC prior to diagnosing DTC B3031.

Step

Action

Yes

No

Schematic Reference: Theft Deterrent System Schematics

1

Did you perform the Vehicle Theft Deterrent (VTD) Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent

2
  1. Install a scan tool.
  2. Momentarily rotate the ignition switch to CRANK. Do not start the vehicle.
  3. Release the ignition switch to ON.
  4. Select the body control module display DTCs function on the scan tool.

Does the scan tool display DTC B3031 as a current DTC?

Go to Step 3

Go to Step 4

3

Does the scan tool display DTC B2947, B2948, B2957, B2958, B2960, or B3033?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition.
  3. Start the vehicle.
  4. Select the body control module display DTCs function on the scan tool.

Does the DTC reset?

Go to Step 3

System OK