For 1990-2009 cars

### 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 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 | B3920 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. When a power seat switch is pressed or when a memory recall is requested, each seat, lumbar, and steering column motor receives battery voltage and ground from the MSM 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, lumbar or steering column in the opposite direction.

### 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.

#### B3920 02

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

#### B3921 01

The voltage on any power rail 2 motor control circuit exceeds 2.78 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 disables all motors in the group for which the DTC was set.

### Conditions for Clearing the DTC

• | The current DTC clears and sets to history when the reference voltage is between 1.47 volts and 2.5 volts for 3 seconds 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

• | Tilt/Telescoping Steering Column Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Power Seats System 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 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 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 column tilt motor terminal 8

• | Steering column tilt motor terminal 7

⇒ | 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 column tilt motor terminal 8

• | Steering column tilt motor terminal 7

⇒ | 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 after completing the diagnostic procedure.

• | Front Seat Recliner Actuator Motor Replacement

• | Front Seat Lumbar Support Replacement

• | Steering Column Replacement

• | Control Module References for the MSM replacement, programming and setup