Power Seat Inoperative w/o Memory-A45

Power seat without memory is completely controlled through the seat adjuster switch. Battery voltage is supplied at all times to the seat adjuster switch from the memory seat module 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.

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

Schematic Reference

Connector End View Reference

Power Seat Connector End Views

Electrical Information Reference

1. Disconnect the harness connector at the seat adjuster switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal B 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 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 seat adjuster switch.
5. Disconnect the harness connector at the appropriate seat motor assembly.
6. Connect a test lamp between the motor control circuit terminals for the inoperative motor.
7. Verify that the test lamp illuminates while pressing the appropriate seat 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 seat adjuster switch.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Power Seat Inoperative w/Memory-A45

A low current battery voltage is supplied at all times to the memory seat module (MSM) from the 10A MSM LOGIC/RF MASSAGE 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 supplied at all times to the MSM from the MSM/LT FRT PWR SEAT 25A circuit breaker. This voltage is connected to power rail 1 internal to the MSM and is used to drive the driver seat adjuster motors, recline motor and the lumbar horizontal motor. Battery positive voltage is also supplied at all times to the MSM from the MSM/T&T 25A circuit breaker. This voltage is connected to power rail 2 and is used to drive the driver seat lumbar vertical motor, passenger seat lumbar vertical motor, and the tilt and telescoping steering column actuators. Each seat and lumbar adjuster motor is controlled by the MSM through 2 motor control circuits. The MSM connects all 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 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 seat switch is operated to move the entire seat forward, battery positive voltage is applied through the switch contacts and the power seat horizontal forward switch signal circuit to the MSM. In response to this signal, the MSM applies battery voltage through the driver seat horizontal motor forward control circuit and ground through the driver seat horizontal motor rearward control circuit to the motor. The motor runs to drive the entire seat forward until the switch is released. Moving the entire seat rearward works similarly to moving the entire seat forward, except that battery positive voltage and ground are applied on the opposite circuits causing the motor to run in the opposite direction.

The scan tool may reference the Memory Seat Module (MSM) as the Driver Position Module.

Schematic Reference

Driver Seat Schematics

Connector End View Reference

Power Seat Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool Driver Position Module seat switch parameters. Verify that none of the seat switch parameters are Active while in an inactive state.

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

2. Observe the scan tool seat switch parameters while pressing and releasing the related seat switch. The reading should change between Inactive and Active.

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

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

Seat Adjuster Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the seat adjuster switch.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal E 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 memory seat module.

3. Install a 3A fused jumper wire between the inoperative switch signal circuit terminal and the B+ circuit terminal E. Verify the related scan tool Driver Position Module Seat Switch parameter is Active.

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

4. If all circuits test normal, test or replace the seat adjuster switch.

Motor Control Circuit Test

1. Disconnect the (C3) harness connector at the memory seat module.
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 memory seat module.
4. Disconnect the (C1) harness connector at the appropriate seat adjuster motor assembly or seat recline motor.
5. Connect a test lamp between the motor control circuit terminals of the inoperative motor.
6. Verify that a test lamp illuminates while pressing the seat 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 memory seat module.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.