Power Seat Inoperative
Power Seat Inoperative
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Battery voltage is supplied at all times to the memory seat module (MSM) from the MDL-MEM 10 A fuse located in the rear 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 supplied at all times to the MSM from the PWR SEAT 25 A circuit breaker located in the I/P fuse block. 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 PWR T/T 25 A circuit breaker also located in the rear fuse block. 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 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 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.
Diagnostic Aids
The scan tool may reference the Memory Seat Module (MSM) as the Driver Position Module.
Reference Information
Schematic Reference
Driver Seat Schematics (Driver Seat Schematics)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Memory Seats Description and Operation (Memory Seats)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Driver Position Module seat switch parameters while pressing the appropriate seat switch. The reading should change between Inactive and Active.
• If the reading does not change between the specified values, refer to the Seat Adjuster Switch Circuit Test.
2. If all seat switch inputs to the MSM function normal, refer to the appropriate test listed below:
* Seat Motor Control Circuit Test
* Recline Motor Control Circuit Test
Circuit/System Testing
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.
3. Verify the scan tool power seat switch parameters are Inactive.
• If not the specified values, test the appropriate signal circuit listed for a short to voltage. If the circuit tests normal, replace the MSM.
* Front vertical down switch terminal K
* Front vertical up switch terminal A
* Horizontal forward switch terminal D
* Horizontal rearward switch terminal C
* Rear vertical down switch terminal J
* Rear vertical up switch terminal F
* Recline forward switch terminal H
* Recline rearward switch terminal G
4. Install a 3 A fused jumper wire between the B+ circuit terminal E and the appropriate signal circuit listed below. Verify the appropriate scan tool seat switch parameter is Active.
* Front vertical down switch terminal K
* Front vertical up switch terminal A
* Horizontal forward switch terminal D
* Horizontal rearward switch terminal C
* Rear vertical down switch terminal J
* Rear vertical up switch terminal F
* Recline forward switch terminal H
* Recline rearward switch terminal G
• If not the specified value, 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 seat adjuster switch.
Seat 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 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. Ignition OFF, connect the X3 harness connector at the MSM and disconnect the X1 harness connector at the seat adjuster motor assembly.
4. Connect a test lamp between the appropriate control circuits listed below.
* Seat horizontal motor terminal 3 and terminal 6
* Seat front vertical motor terminal 2 and terminal 5
* Seat rear vertical motor terminal 1 and terminal 4
5. Ignition ON, command the appropriate seat 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 seat motor.
Recline Motor Control Circuit Test
1. Ignition OFF, disconnect the harness connector at the recline motor.
2. Connect a test lamp between control circuit terminal A and control circuit terminal B.
3. Ignition ON, command the Recline Forward/Rearward with a scan tool. The test lamp should turn ON when commanding the 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.
4. If all circuits test normal, test or replace the recline motor.
Component Testing
Seat Adjuster Switch Test
1. Ignition OFF, disconnect the harness connector at the seat adjuster switch.
2. Test for infinite resistance between the B+ terminal E and the switch terminals listed below and with the switch in the open position.
* Front vertical upward switch terminal A
* Front vertical downward switch terminal K
* Rear vertical upward switch terminal F
* Rear vertical downward switch terminal J
* Horizontal forward switch terminal D
* Horizontal rearward switch terminal C
* Recline forward switch terminal H
* Recline rearward switch terminal G
• If not the specified value, replace the seat adjuster switch.
3. Test for less than 1 ohm between the B+ terminal E and each the switch terminals listed below with the appropriate switch in the closed position.
* Front vertical upward switch terminal A
* Front vertical downward switch terminal K
* Rear vertical upward switch terminal F
* Rear vertical downward switch terminal J
* Horizontal forward switch terminal D
* Horizontal rearward switch terminal C
* Recline forward switch terminal H
* Recline rearward switch terminal G
• If greater than the specified range, replace the seat adjuster switch.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Power Seat Switch Replacement (Power Seat Switch Replacement)
* Front Seat Adjuster Replacement (Front Seat Adjuster Replacement)
* Front Seat Recliner Actuator Motor Replacement (Front Seat Recliner Actuator Motor Replacement)
* Control Module References (Programming and Relearning)for MSM replacement, setup, and programming