Buick Regal: DTC B3920

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC B3920

Seat Motors Group 1 Ground Circuit

For symptom byte information refer to Symptom Byte List.

Diagnostic Fault Information

1. All power seat and memory functions are inoperative.

Circuit/System Description

The seat memory control module controls the seat motors via half bridges that are connected to a power rail internal to the module. The seat memory control module connects all of the motor control circuits on the power rail to a common reference point whenever they are not in operation. The module monitors all seat motor control circuits for a shorted to ground or voltage before enabling any seat motor.

When a power seat switch is pressed or when a memory recall is requested, each seat motor receives battery voltage and ground from the seat memory control module via the motor control circuits. All motors are reversible, so the direction the motor rotates depends on which control circuit voltage is applied and which control circuit ground is applied. When the switch is operated in the opposite direction, the module reverses the polarity and applies voltage and ground to the opposite circuits to move the seat in the opposite direction.

Conditions for Running the DTC

• DTC B1325 must not be present.
• Module battery voltage must be between 9 - 16 V.

Conditions for Setting the DTC

B3920 00

Current out of the module does not match the current returning to the module from 1.5 - 5 A.

B3920 01

The voltage on any power rail 1 motor control circuit exceeds 2.78 V for 100 ms.

B3920 02

The voltage on any power rail 1 motor control circuit is below 1.47 V for 100 ms.

B3920 0B

The differential current measured through the high and low side of the power rail is within tolerance of each other, but the absolute current or an over-current has exceeded the maximum value.

Action Taken When the DTC Sets

The seat memory control module will not allow operation of any motor on the power rail for which the DTC was set.

Conditions for Clearing the DTC

• The current DTC clears when the fault is no longer present and the power mode changes to ignition OFF then back to ignition ON.
• The history DTC will clear after 40 consecutive fault-free ignition cycles have occurred.

Reference Information

Schematic Reference

• Driver Seat Wiring Schematics
• Passenger Seat Wiring Schematics

Connector End View Reference

Component Connector End View Index

Description and Operation

Memory Seats Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Testing

B3920 01 or B3920 02

1. Ignition OFF, disconnect the X3 harness connector at the appropriate seat memory control module listed below:

• K40D Seat Memory Control Module - Driver
• K40P Seat Memory Control Module - Passenger

2. Test for infinite resistance between each control circuit terminal listed below and ground:

• Seat front vertical motor up control terminal 3
• Seat front vertical motor down control terminal 4
• Seat rear vertical motor up control terminal 5
• Seat rear vertical motor down control terminal 6
• Seat horizontal motor forward control terminal 11
• Seat horizontal motor rearward control terminal 12
• Seat recline motor forward control terminal 1
• Seat recline motor rearward control terminal 2
• If less than infinite resistance

Repair the short to ground on the circuit.

• Go to next step: If infinite resistance

3. Ignition ON.

4. Test for less than 1 V between each control circuit terminal listed below and ground:

• Seat front vertical motor up control terminal 3
• Seat front vertical motor down control terminal 4
• Seat rear vertical motor up control terminal 5
• Seat rear vertical motor down control terminal 6
• Seat horizontal motor forward control terminal 11
• Seat horizontal motor rearward control terminal 12
• Seat recline motor forward control terminal 1
• Seat recline motor rearward control terminal 2
• If 1 V or greater

Repair the short to voltage on the circuit.

• Go to next step: If less than 1 V

5. Replace the K40 Seat Memory Control Module.

B3920 00 or B3920 0B

1. Ignition ON.

2. Clear the current and history DTC.

3. Determine which motor set this DTC by operating each seat motor listed below one at a time in both directions. Check for the DTC to set between each motor test.

• M50 Seat Front Vertical Motor
• M55 Seat Rear Vertical Motor
• M51 Seat Horizontal Motor
• M56 Seat Recline Motor

4. Ignition OFF, disconnect the harness connector at the seat motor for which the DTC set, ignition ON.

5. Clear the DTC.

6. Verify that DTC B3920 00 or B3920 0B does not set while operating the seat motor adjuster switch in both directions.

• If DTC B3920 00 or B3920 0B sets

1. Ignition OFF.
2. Test for infinite resistance between control circuit terminal 1 and control circuit terminal 3.
   • If less than infinite resistance, repair the short between the circuits.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in each control circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K40 Seat Memory Control Module.

• Go to next step: If DTC B3920 00 or B3920 0B does not set

7. Test or replace the seat motor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Front Seat Tilt Adjuster Actuator Replacement
• Driver or Passenger Seat Vertical Adjuster Actuator Replacement
• Driver or Passenger Seat Recliner Actuator Replacement (Except GS) or Driver or Passenger Seat Recliner Actuator Replacement (GS)
• Control Module References for K40D Seat Memory Control Module - Driver or K40P Seat Memory Control Module - Passenger replacement, programming and setup

READ NEXT: