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 00: Group 1 Seat Motors Common Circuit Malfunction
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 B3920 42: Group 1 Seat Motors Common Circuit Calibration Not Programmed
DTC B3920 0B: Group 1 Seat Motors Common Circuit High Current

### 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 | --
Driver Seat Front Vertical Motor Up Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Rear Vertical Motor Down Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Rear Vertical Motor Up Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Horizontal Motor Forward Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Horizontal Motor Rearward Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Recline Motor Forward Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
Driver Seat Recline Motor Rearward Control | B3920 02 | B1335 0B | 1 | B3920 01 | --
1. Power seat motor inoperative

### Circuit/System Description

The memory seat module controls the seat motors via half bridges that are connected to power rails internal to the module. The memory seat module 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 memory seat module checks to see if this reference voltage is shorted to ground or battery before enabling any seat motor.

When a power seat switch is pressed or when a memory recall is requested, each seat motor receives battery voltage and ground from the memory seat module 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 in the opposite direction.

### Conditions for Running the DTC

• | DTC B1325 must not be present.

• | Module battery voltage must be between 9 - 16 V.

### Conditions for Setting the DTC

#### B3920 00

Current out of the module does not match the current returning to the module from 1.5 - 5 A.

#### 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.

#### B3920 42

This DTC will set if the module calibration is not programmed.

#### B3920 0B

The differential current measured through the high and low side of the power rail is within tolerance of each other, but the absolute current or an over-current has exceeded the maximum value.

### Action Taken When the DTC Sets

The memory seat module 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 fault is no longer present and the power mode changes to OFF then back to ACC or RUN.

• | The history DTC will clear after 40 consecutive fault-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Driver Seat Schematics

#### Connector End View Reference

Component Connector End Views

#### 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 X4, X5 harness connectors at the K40 memory seat module.
2. Test for infinite resistance between the control circuit terminals listed below and ground:

• | M50D front vertical motor up control terminal 7 X4

• | M50D front vertical motor down control terminal 8 X4

• | M55D rear vertical motor up control terminal 4 X5

• | M55D rear vertical motor down control terminal 3 X5

• | M51D horizontal motor forward control terminal 2 X5

• | M51D horizontal motor rearward control terminal 1 X5

• | M56D recline motor forward control terminal 5 X5

• | M56D recline motor rearward control terminal 6 X5

⇒ | If not the specified value, test the control circuit for a short to ground.

3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminals listed below and ground:

• | M50D front vertical motor up control terminal 7 X4

• | M50D front vertical motor down control terminal 8 X4

• | M55D rear vertical motor up control terminal 4 X5

• | M55D rear vertical motor down control terminal 3 X5

• | M51D horizontal motor forward control terminal 2 X5

• | M51D horizontal motor rearward control terminal 1 X5

• | M56D recline motor forward control terminal 5 X5

• | M56D recline motor rearward control terminal 6 X5

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

4. If all circuits test normal, replace the K40 memory seat module.

#### B3920 00 or B3920 0B

1. Ignition ON, use a scan tool to clear the current and history DTC.
2. Determine which motor set this DTC by operating the seat motors listed below one at a time in both directions. Check for the DTC to set between each motor test.

• | M50D front vertical motor

• | M55D rear vertical motor

• | M51D horizontal motor

• | M56D recline motor

3. Clear the diagnostic trouble code.
4. Ignition OFF, disconnect the harness connector at the appropriate seat motor for which the DTC set.
5. Ignition ON, operate the appropriate motor adjuster switch in both directions. DTC B3920 00 or B3920 0B should not set.

⇒ | If the DTC sets, test for a short between control circuits terminal 1 and terminal 5. If the circuits test normal, replace the K40 memory seat module.

6. Test control circuits terminal 1 and terminal 5 for a high resistance. If the circuits test normal, test or replace the seat motor.

#### B3920 42

If this DTC is set, replace the K40 memory seat module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Front Seat Recliner Actuator Motor Replacement

• | Front Seat Adjuster Motor Replacement

• | Control Module References for memory seat module replacement, setup, and programming