Lumbar Support Inoperative w/o Memory-A45

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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 from the MSM/RT FRT PWR SEAT 25A circuit breaker that is located in the rear fuse block. When the seat adjuster 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.

Schematic Reference

Passenger Seat Schematics

Connector End View Reference

Power Seat Connector End Views

Electrical Information Reference

1. Disconnect the harness connector at the lumbar adjuster switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal E and ground.

⇒	If greater than 1 ohm, test the ground circuit for an open/high resistance.

3. 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. Connect the harness connector at the lumbar adjuster switch.
5. Disconnect the harness connector at the lumbar motor assembly.
6. Connect a test lamp across the motor control circuit terminals for the inoperative motor.
7. Verify that the test lamp illuminates while pressing the lumbar switch in both directions.

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

8. If the circuits test normal replace the lumbar motor assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Lumbar Support Inoperative with Memory-A45

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

A low current battery voltage is supplied at all times to the memory seat module (MSM) from the 10A MSM LOGIC fuse. 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 MSM/LT FRT PWR SEAT 25A circuit breaker. 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.

All 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.

Schematic Reference

Connector End View Reference

Power Seat Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool Memory Seat Module Lumbar Switch parameters while pressing the related lumbar switch. The reading should change between Inactive and Active.
2. Verify that none of the Lumbar Switch parameters are Active while the switch is in an inactive state.

⇒	If any of the switch parameters are Active, perform the Switch Circuit Test.

3. Verify that the Lumbar Switch parameters are Active while the switch is pressed.

⇒	If any of the switch parameters are not Active, perform the Switch Circuit Test.

4. If all lumbar switch inputs to the MSM function normal, preform the Motor Control Circuit Test.

Lumbar Adjuster 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 input parameters are Inactive.

⇒	If not Inactive, test the appropriate signal circuit for a short to voltage. If the circuit tests normal, replace the memory seat module.

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

⇒	If not Active, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the MSM.

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

Motor Control Circuit Test

1. Disconnect the (C3) harness connector at the MSM.
2. Verify that a test lamp illuminates between the B+ circuit terminal 5 and ground.

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

3. Connect the (C3) harness connector at the MSM.
4. Disconnect the (C1) harness connector at the seat lumbar motor assembly.
5. Connect a test lamp between the motor control circuit terminals of the inoperative motor.
6. The test lamp should illuminate while pressing the switch in both directions.

⇒	If the test lamp does not illuminate, test the motor control circuits for an open/high resistance. If the circuits test normal replace the MSM.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.