For 1990-2009 cars

## Lumbar Support Inoperative With Memory A45

### 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.

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
B+ MSM Terminal 2 X3 | 1 | 1 | 1 | -- | --
B+ Lumbar Adjuster Switch | 2 | 1 | 1 | -- | --
Lumbar Down Switch Signal | 2 | 1 | 1 | -- | --
Lumbar Up Switch Signal | 2 | 1 | 1 | -- | --
Lumbar Forward Switch Signal | 2 | 1 | 1 | -- | --
Lumbar Rearward Switch Signal | 2 | 1 | 1 | -- | --
Driver Seat Lumbar Motor Forward Control | B3920 02 | B1335 00, B1335 0B | 1 | B3920 01 | B1335 42, B1335 4B, B1850 5A
Driver Seat Lumbar Motor Rearward Control | B3920 02 | B1335 00, B1335 0B | 1 | B3920 01 | B1335 42, B1335 4B, B1850 5A
Driver Seat Lumbar Motor Down Control | B3921 02 | B1340 00, B1340 0B | 1 | B3921 01 | B1340 42, B1340 4B, B1860 5A
Driver Seat Lumbar Motor Up Control | B3921 02 | B1340 00, B1340 0B | 1 | B3921 01 | B1340 42, B1340 4B, B1860 5A
1. Lumbar support inoperative 2. Scan Tool Does Not Communicate with Low Speed GMLAN Device

### Circuit/System Description

Battery voltage is supplied at all times to the memory seat module (MSM) from the MSM 10A fuse located in the I/P fuse block. This voltage is used by the MSM for logic power and to supply battery reference voltage to the seat and lumbar adjuster switches. Battery positive voltage is also supplied at all times to the MSM from the LT/PWR/SEAT 25A circuit breaker also located in the I/P fuse block. This voltage is connected to a power rail internal to the MSM and is used to drive the power seat motors, lumbar motors, and seat heater elements on vehicles equipped with heated seats. Each seat and lumbar adjuster motor is controlled by the MSM through 2 motor control circuits. The MSM connects all motor control circuits on the 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 the reference voltage is shorted to ground or battery before enabling any of the seat or lumbar motors.

Both lumbar motors are reversible. For example, when the lumbar switch is operated to move the lumbar support forward, battery positive voltage is applied through the switch contacts and the lumbar horizontal forward switch signal circuit to the MSM. In response to this signal, the MSM applies battery voltage through the lumbar motor forward control circuit and ground through the lumbar motor rearward control circuit to the motor. The motor runs to drive the lumbar support forward toward the occupants back until the switch is released. Moving the lumbar support rearward works similarly to moving the lumbar support forward, except that battery positive voltage and ground are applied on the opposite circuits causing the motor to run in the opposite direction. The lumbar support vertical motor is also powered this way.

### Reference Information

#### Schematic Reference

• | Driver Seat Schematics

• | Passenger Seat Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Lumbar Support 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 Verification

1. Ignition ON, verify that all manual power seat functions operate when being controlled by the seat adjuster switches.

⇒ | If all seat functions do not operate, refer to Power Seat Inoperative.

2. Ignition ON, observe the scan tool Memory Seat Module lumbar switch parameters while pressing the appropriate lumbar switch. The reading should change between Inactive and Active.

⇒ | If the reading does not change between the specified values, refer to the Lumbar Switch Circuit Test.

3. If all lumbar switch inputs to the MSM function normal, refer to the Lumbar Motor Control Circuit Test.

### Circuit/System Testing

#### Lumbar Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the lumbar adjuster switch.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal G and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the MSM.

3. Verify that all scan tool lumbar switch parameters are Inactive.

⇒ | If not the specified value, test the appropriate signal circuits listed below for a short to voltage. If the circuit tests normal, replace the MSM.

• | Lumbar horizontal forward terminal A

• | Lumbar horizontal rearward terminal F

• | Lumbar vertical upward terminal C

• | Lumbar vertical downward terminal B

4. Install a 3A fused jumper wire between the appropriate signal circuit listed below and the B+ circuit terminal G. Verify the scan tool Lumbar Switch parameter is Active.

• | Lumbar horizontal forward terminal A

• | Lumbar horizontal rearward terminal F

• | Lumbar vertical upward terminal C

• | Lumbar vertical downward terminal B

⇒ | If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the MSM.

5. If all circuits test normal, test or replace the lumbar switch.

#### Lumbar Motor Control Circuit Test

1. Ignition OFF, disconnect the X3 harness connector at the MSM.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 2 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the X3 harness connector at the MSM and disconnect the harness connector at the appropriate lumbar motor.
4. Connect a test lamp between control circuit terminal 1 and control circuit terminal 5.
5. Ignition ON, command the appropriate lumbar motor in the Up/Down or Forward/Rearward directions with a scan tool. The test lamp should turn ON when commanding the up and down or forward and rearward states.

⇒ | If the test lamp remains OFF during either of the commands, test the control circuits for an open/high resistance. If the circuits test normal replace the MSM.

6. If all circuits test normal, test or replace the lumbar motor.

### Component Testing

#### Lumbar Switch

1. Ignition OFF, disconnect the harness connector at the lumbar switch.
2. Test for infinite resistance between each seat direction signal terminal listed below and the B+ terminal G with the switch in the open position.

• | Lumbar vertical upward switch terminal C

• | Lumbar vertical downward switch terminal B

• | Lumbar horizontal forward switch terminal A

• | Lumbar horizontal rearward switch terminal F

⇒ | If not the specified value, replace the lumbar switch.

3. Test for less than 1 ohm between each lumbar direction signal terminal listed below and the B+ terminal G with the switch in the closed position.

• | Lumbar vertical upward switch terminal C

• | Lumbar vertical downward switch terminal B

• | Lumbar horizontal forward switch terminal A

• | Lumbar horizontal rearward switch terminal F

⇒ | If greater than the specified range, replace the lumbar switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Front Seat Lumbar Control Switch Replacement

• | Front Seat Lumbar Support Replacement

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

## Lumbar Support Inoperative Without Memory A45

### 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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
B+ Lumbar Switch | 1, 2 | 2 | -- | --
Lumbar Motor Up Control | 2 | 2 | -- | --
Lumbar Motor Down Control | 2 | 2 | -- | --
Lumbar Motor Rearward Control | 2 | 2 | -- | --
Lumbar Motor Forward Control | 2 | 2 | -- | --
Ground - Lumbar Switch | -- | 2 | -- | --

1. Power seats inoperative
2. Lumbar support inoperative

### Circuit/System Description

Power seat lumbar support without memory is completely controlled through the seat lumbar adjuster switch. Battery voltage is supplied at all times to the seat lumbar adjuster switch through the LT/PWR/SEAT circuit breaker or the RT/PWR/SEAT circuit breaker that are located in the I/P fuse block. When the lumbar switches are in an inactive state, the switch contacts are closed to the switch ground circuit.

Both lumbar motors are reversible. For example, when the lumbar horizontal forward switch is pressed to move the lumbar support forward, battery voltage is applied through the switch contacts and the lumbar motor forward control circuit to the motor. The motor is grounded through the lumbar motor rearward switch contacts and the lumbar motor rearward control circuit to the motor. The motor runs in order to drive the lumbar support forward toward the occupants back until the switch is released. Moving the lumbar support rearward works similarly to moving the lumbar support forward, except that battery positive voltage and ground are applied on opposite circuits causing the motor to run in the opposite direction. The lumbar support vertical motor is also powered this way.

### Reference Information

#### Schematic Reference

• | Driver Seat Schematics

• | Passenger Seat Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Lumbar Support Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the lumbar switch.
2. Test for less than 1 ohm between the ground circuit terminal E and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal G and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. Ignition OFF, connect the harness connector at the lumbar switch and disconnect the harness connector at the appropriate lumbar motor.
5. Ignition ON, verify that the test lamp illuminates between control circuit terminal A and control circuit terminal B while pressing the lumbar switch in both directions.

⇒ | If the test lamp does not illuminate for both directions, test the control circuits for a short to ground or an open/high resistance. If the circuits test normal, test or replace the lumbar switch.

6. If all circuits test normal, test or replace the lumbar motor.

### Component Testing

#### Lumbar Switch

1. Ignition OFF, disconnect the harness connector at the lumbar switch.
2. Test for infinite resistance between each seat direction signal terminal listed below and the B+ terminal G with the switch in the open position.

• | Lumbar vertical upward switch terminal C

• | Lumbar vertical downward switch terminal B

• | Lumbar horizontal forward switch terminal A

• | Lumbar horizontal rearward switch terminal F

⇒ | If not the specified value, replace the lumbar switch.

3. Test for less than 1 ohm between each lumbar direction signal terminal listed below and the B+ terminal G with the switch in the closed position.

• | Lumbar vertical upward switch terminal C

• | Lumbar vertical downward switch terminal B

• | Lumbar horizontal forward switch terminal A

• | Lumbar horizontal rearward switch terminal F

⇒ | If greater than the specified range, replace the lumbar switch.

4. Test for less than 1 ohm between each lumbar direction signal terminal listed below and the ground terminal E with the switch in the open position

• | Lumbar vertical upward switch terminal C

• | Lumbar vertical downward switch terminal B

• | Lumbar horizontal forward switch terminal A

• | Lumbar horizontal rearward switch terminal F

⇒ | If greater than the specified range, replace the lumbar switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Front Seat Lumbar Control Switch Replacement

• | Front Seat Lumbar Support Replacement