Coupe
DTC B3920 or B3921 (Coupe)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC B3920 01
- Group 1 Seat Motors Common Circuit Short to Battery
DTC B3920 02
- Group 1 Seat Motors Common Circuit Short to Ground
DTC B3921 01
- Group 2 Seat Motors Common Circuit Short to Battery
DTC B3921 02
- Group 2 Seat Motors Common Circuit Short to Ground
Diagnostic Fault Information
Circuit/System Description
The memory seat module (MSM) controls the driver seat, recline, lumbar motors, the passenger seat horizontal motor, and the steering column motors via half bridges that are divided into 2 groups. Each group is connected to separate power rail internal to the module. The MSM connects all of the motor control circuits on each power rail to a common reference point whenever they are not in operation. This reference point is biased to approximately 2.5 V. The MSM checks to see if this reference voltage is shorted to ground or battery before enabling any seat, lumbar, or steering column motor.
Conditions for Running the DTC
The MSM must be powered.
Conditions for Setting the DTC
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.
B3921 01
The voltage on any power rail 2 motor control circuit exceeds 2.78 V for 100 ms.
B3921 02
The voltage on any power rail 2 motor control circuit is below 1.47 V for 100 ms.
Action Taken When the DTC Sets
The MSM 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 malfunction is no longer present and the power mode changes to OFF then back to ACC or RUN.
* The history DTC will clear after 50 consecutive fault-free ignition cycles have occurred.
Reference Information
Schematic Reference
* Driver Seat Schematics Driver Seat Schematics
* Passenger Seat Schematics Passenger Seat Schematics
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
Memory Seats Description and Operation Memory Seats
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Testing
B3920 01 or B3920 02
1. Ignition OFF, disconnect the X1 harness connector at the MSM.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:
* Driver seat front vertical motor terminal 12
* Driver seat front vertical motor terminal 13
* Driver sea rear vertical motor terminal 15
* Driver seat rear vertical motor terminal 16
* Driver seat horizontal motor terminal 9
* Driver seat horizontal motor terminal 10
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Test for infinite resistance between the control circuits listed below and ground:
* Driver seat front vertical motor terminal 12
* Driver seat front vertical motor terminal 13
* Driver sea rear vertical motor terminal 15
* Driver seat rear vertical motor terminal 16
* Driver seat horizontal motor terminal 9
* Driver seat horizontal motor terminal 10
• If not the specified value, test the control circuit for a short to ground.
4. Ignition OFF, disconnect the X4 harness connector at the MSM.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:
* Driver seat lumbar horizontal motor terminal 12
* Driver seat lumbar horizontal motor terminal 13
* Driver seat recline motor terminal 15
* Driver seat recline motor terminal 16
* Passenger seat horizontal motor terminal 9
* Passenger seat horizontal motor terminal 10
• If the test lamp illuminates, test the control circuit for a short to voltage.
6. Test for infinite resistance between the control circuits listed below and ground:
* Driver seat lumbar horizontal motor terminal 12
* Driver seat lumbar horizontal motor terminal 13
* Driver seat recline motor terminal 15
* Driver seat recline motor terminal 16
* Passenger seat horizontal motor terminal 9
* Passenger seat horizontal motor terminal 10
• If not the specified value, test the control circuit for a short to ground.
7. If all circuits test normal, replace the MSM.
B3921 01 or B3921 02
1. Ignition OFF, disconnect the X1 harness connector at the MSM.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:
* Steering column telescope motor terminal 7
* Steering column telescope motor terminal 8
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Test for infinite resistance between the control circuits listed below and ground:
* Steering column telescope motor terminal 7
* Steering column telescope motor terminal 8
• If not the specified value, test the control circuit for a short to ground.
4. Ignition OFF, disconnect the X4 harness connector at the MSM.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:
* Steering column tilt motor terminal 7
* Steering column tilt motor terminal 8
• If the test lamp illuminates, test the control circuit for a short to voltage.
6. Test for infinite resistance between the control circuits listed below and ground:
* Steering column tilt motor terminal 7
* Steering column tilt motor terminal 8
• If not the specified value, test the control circuit for a short to ground.
7. If all circuits test normal, replace the MSM.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Front Seat Tilt Adjuster Actuator Replacement Front Seat Tilt Adjuster Actuator Replacement
* Front Seat Adjuster Actuator Replacement Front Seat Adjuster Actuator Replacement
* Driver Seat Outer Adjuster Rear Vertical Actuator Replacement Driver Seat Outer Adjuster Rear Vertical Actuator Replacement
* Seat Lumbar Sub System Replacement (AQ9) Seat Lumbar Sub System Replacement (AQ9)Seat Lumbar Sub System Replacement (W2E) Seat Lumbar Sub System Replacement (W2E)
* Front Seat Recliner Actuator Motor Replacement Front Seat Recliner Actuator Motor Replacement
* Steering Column Replacement Steering Column Replacement
* Control Module References Control Module References for MSM replacement, setup, and programming