B3921
DTC B3920 or B3921
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, adjustable pedal, and tilt steering wheel motors via half bridges that are divided into 2 groups that are connected to separate power rails internal to the module. The MSM connects all of the motor control circuits 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, adjustable pedal, or steering wheel 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.
* A 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
* Adjustable Pedal Schematics Electrical Diagrams
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:
* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* 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:
* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* 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:
* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
* Adjustable pedal actuator terminal 9
* Adjustable pedal actuator 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:
* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
* Adjustable pedal actuator terminal 9
* Adjustable pedal actuator 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 X4 harness connector at the MSM.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:
* Lumbar vertical motor terminal 1
* Lumbar vertical motor terminal 2
* Steering wheel tilt actuator terminal 7
* Steering wheel tilt actuator 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:
* Lumbar vertical motor terminal 1
* Lumbar vertical motor terminal 2
* Steering wheel tilt actuator terminal 7
* Steering wheel tilt actuator terminal 8
• If not the specified value, test the control circuit for a short to ground.
4. If all circuits test normal, replace the MSM.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Front Seat Adjuster Replacement (without HP2) Front Seat Adjuster ReplacementFront Seat Adjuster Replacement (with HP2) Front Seat Adjuster Replacement
* Front Seat Recliner Actuator Motor Replacement Front Seat Recliner Actuator Motor Replacement
* Seat Lumbar Sub System Replacement Seat Lumbar Sub System Replacement
* Brake Pedal Assembly Replacement Brake Pedal Assembly Replacement
* Control Module References Control Module References for the MSM replacement, programming and setup