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B3920




DTC B3920 or B3921 (Sedan, Wagon)

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 seat, recline, lumbar, and steering column 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 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 End Views By Name)
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 (Programming and Relearning) 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

• 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

• 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 (without AHS) (Seat Lumbar Sub System Replacement (without AHS))Seat Lumbar Sub System Replacement (with AHS) (Seat Lumbar Sub System Replacement (with AHS))
* Front Seat Recliner Actuator Motor Replacement (Front Seat Recliner Actuator Motor Replacement)
* Steering Column Replacement (Steering Column Replacement)
* Control Module References (Programming and Relearning) for MSM replacement, setup, and programming

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