Diagnostic Instructions

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	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
Driver Seat Front Vertical Motor Down Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2355 5A
Driver Seat Front Vertical Motor Up Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2355 5A
Driver Seat Rear Vertical Motor Down Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2365 5A
Driver Seat Rear Vertical Motor Up Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2365 5A
Driver Seat Horizontal Motor Forward Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2375 5A
Driver Seat Horizontal Motor Rearward Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B2375 5A
Driver Seat Recline Motor Forward Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B1825 5A
Driver Seat Recline Motor Rearward Control	B3920 02	B1335 0B	1	B3920 01	B1335 42, B1335 4B, B1825 5A
Driver Seat Lumbar Motor Up Control	B3921 02	B1340 0B	2	B3921 01	B1340 42, B1340 4B, B1860 5A
Driver Seat Lumbar Motor Down Control	B3921 02	B1340 0B	2	B3921 01	B1340 42, B1340 4B, B1860 5A
Driver Seat Lumbar Motor Forward Control	B3920 02	B1335 0B	2	B3920 01	B1335 42, B1335 4B, B1850 5A
Driver Seat Lumbar Motor Rearward Control	B3920 02	B1335 0B	2	B3920 01	B1335 42, B1335 4B, B1850 5A
Steering Column Telescope Motor Forward Control	B3921 02	B1340 0B	3	B3921 01	B1340 42, B1340 4B, B2860 5A
Steering Column Telescope Motor Rearward Control	B3921 02	B1340 0B	3	B3921 01	B1340 42, B1340 4B, B2860 5A
Steering Column Tilt Motor Down Control	B3921 02	B1340 0B	3	B3921 01	B1340 42, B1340 4B, B2880 5A
Steering Column Tilt Motor Up Control	B3921 02	B1340 0B	3	B3921 01	B1340 42, B1340 4B, B2880 5A
1. Power seat motor inoperative 2. Lumbar motor inoperative 3. Tilt or telescope steering column motor inoperative

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 volts. 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 volts for 100 ms.

B3921 01

The voltage on any power rail 2 motor control circuit exceeds 2.78 volts for 100 ms.

B3920 02

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

B3921 02

The voltage on any power rail 2 motor control circuit is below 1.47 volts 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

Reference Information

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Memory Seats Description and Operation

Electrical Information Reference

Scan Tool Reference

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

⇒	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:

•	Lumbar vertical motor terminal 1

•	Lumbar vertical motor terminal 2

•	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:

•	Lumbar vertical motor terminal 1

•	Lumbar vertical motor terminal 2

•	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 after completing the diagnostic procedure.