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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Envoy - 2WD 🢒 Seats 🢒 Power Seats 🢒 Power Seat Inoperative

Power Seat 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

Seat Adjuster Switch B+

1

1

--

--

Front Vertical Motor Down Control

1

1

--

--

Front Vertical Motor Up Control

1

1

--

--

Horizontal Motor Forward Control

1

1

--

--

Horizontal Motor Rearward Control

1

1

--

--

Rear Vertical Motor Down Control

1

1

--

--

Rear Vertical Motor Up Control

1

1

--

--

Recline Motor Forward Control

1

1

--

--

Recline Motor Rearward Control

1

1

--

--

Seat Adjuster Switch Ground

--

1

--

--

1. Power seat inoperative

Circuit/System Description

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 30A SEATS 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 and G302.

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.

Reference Information

Schematic Reference

    •  Driver Seat Schematics
    •  Passenger Seat Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Power Seats System 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

Operate the switches for the seat directional motors listed below in both directions. The seat should move in the commanded directions.

    • Seat front vertical motor
    • Seat rear vertical motor
    • Seat horizontal motor
    • Seat recline motor
⇒If the power seat is inoperative in all directions, refer to the Seat Adjuster Switch Circuit Test.
⇒If 1 or more of the seat adjuster motors operate, refer to the Seat Adjuster Motor Circuit Test.

Circuit/System Testing

Seat Adjuster Switch Circuit Test

  1. Ignition OFF, disconnect the harness connector at the seat adjuster switch.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground:
    3. • Driver seat adjuster switch terminal B
    • Passenger seat adjuster switch terminal D
    ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the appropriate B+ circuit terminal listed below and ground:
    4. • Driver seat adjuster switch terminal E
    • Passenger seat adjuster switch terminal A
    ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. If all circuits test normal, test or replace the seat adjuster switch.

Adjuster Motor Control Circuit Test

  1. Ignition OFF, disconnect the harness connector at the appropriate seat motor.
  2. Connect a test lamp between control circuit terminal A and control circuit terminal B.
  3. Operate the appropriate seat switch in both directions. The test lamp should turn ON when commanding the motor in both directions.
    4. ⇒If the test lamp remains OFF during either of the commands, test the control circuits for a short to ground or an open/high resistance. If the circuits test normal, test or replace the seat adjuster switch.
  4. If all circuits test normal, test or replace the appropriate seat motor.

Component Testing

Seat Adjuster Switch

  1. Ignition OFF, disconnect the harness connector at the seat adjuster switch.
  2. Test for infinite resistance between each control terminal and the B+ terminal with the switch in the open position.
    3. ⇒If not the specified value, replace the seat adjuster switch.
  3. Test for less than 1 ohm between each control terminal and the B+ terminal with the switch in the closed position.
    4. ⇒If greater than the specified range, replace the seat adjuster switch.
  4. Test for less than 1 ohm between each control terminal and the ground terminal with the switch in the open position.
    5. ⇒If greater than the specified range, replace the seat adjuster switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Power Seat Switch Replacement
    •  Front Seat Lumbar Control Switch Replacement
    •  Power Seat Adjuster Mechanism Replacement
    •  Front Seat Lumbar Support Replacement

Power Seat 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

Open/High Resistance

Short to Voltage

Signal Performance

B+ MSM Terminal C X1

1

1

--

--

B+ MSM Terminal A1 X4

2

2

--

--

B+ Seat Adjuster Switch

2

1

--

--

Front Vertical Up Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Front Vertical Down Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Horizontal Forward Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Horizontal Rearward Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Rear Vertical Down Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Rear Vertical Up Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Recline Forward Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Recline Rearward Switch Signal

2

1

B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820

--

Driver Seat Front Vertical Motor Down Control

1

1

--

--

Driver Seat Front Vertical Motor Up Control

1

1

--

--

Driver Seat Horizontal Motor Forward Control

1

1

--

--

Driver Seat Horizontal Motor Rearward Control

1

1

--

--

Driver Seat Rear Vertical Motor Down Control

1

1

--

--

Driver Seat Rear Vertical Motor Up Control

1

1

--

--

Driver Seat Recline Motor Forward Control

1

1

--

--

Driver Seat Recline Motor Rearward Control

1

1

--

--

Ground - Seat Adjuster Switch

--

3

--

--

Ground - MSM

--

2

--

--

1. Power seat inoperative

2. Scan Tool Does Not Communicate with Low Speed GMLAN Device

3. No effect

Circuit/System Description

Battery voltage is supplied at all times to the memory seat module (MSM) from the 10A LGM/DSM fuse located in the rear fuse block. This voltage is used by the MSM for logic power and to supply battery voltage to the seat and lumbar adjuster switches. Battery voltage is supplied at all times to the MSM from the SEATS 30A circuit breaker located in the rear fuse block. This voltage is used by the MSM to drive the driver seat adjuster motors, recline motor and the lumbar motor.

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

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 Verification
  1. Ignition ON, observe the scan tool seat adjuster switch parameters while operating each adjuster switch in both directions. The reading should change between Inactive and the desired direction.
    2. ⇒If any of the switch input parameters are Inactive or Invalid while the switch is pressed, refer to the Seat Adjuster Switch Circuit Test
  2. If all seat switch inputs to the MSM function normal, refer to Seat 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.
    3. ⇒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 seat switch parameters listed below are Inactive:
    4. • Recline Switch
    • Horizontal Position Switch
    • Rear Vertical Position Switch
    • Front Vertical Position Switch
    ⇒If not the specified value, test the appropriate signal circuit listed below for a short to voltage. If the circuit tests normal, replace the MSM.
    • Front vertical up switch terminal K
    • Front vertical down switch terminal J
    • Rear vertical up switch terminal H
    • Rear vertical down switch terminal G
    • Horizontal forward switch terminal D
    • Horizontal rearward switch terminal C
    • Recline forward switch terminal F
    • Recline rearward switch terminal A
  4. Install a 3A fused jumper wire between the appropriate signal circuit listed below and the B+ circuit terminal E. Verify the appropriate scan tool seat position switch parameter is Forward/Rearward or Up/Down.
    5. • Front vertical up switch terminal K
    • Front vertical down switch terminal J
    • Rear vertical up switch terminal H
    • Rear vertical down switch terminal G
    • Horizontal forward switch terminal D
    • Horizontal rearward switch terminal C
    • Recline forward switch terminal F
    • Recline rearward switch terminal A
    ⇒If not the specified value, test the signal circuit for 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 seat adjuster switch.

Seat Motor Control Circuit Test

  1. Ignition OFF, disconnect the X1 harness connector at the MSM.
  2. Verify that a test lamp illuminates between the B+ circuit terminal C and ground.
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Connect the X1 harness connector at the MSM and disconnect the harness connector at the appropriate seat motor.
  4. Connect a test lamp between control circuit terminal A and control circuit terminal B.
  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.
    6. ⇒If the test lamp remains OFF during either of the commands, test the control circuits for a short to ground or an open/high resistance. If the circuits test normal replace the MSM.
  6. If all circuits test normal, test or replace the seat 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 each seat direction signal terminal listed below and the B+ terminal E with the switch in the open position.
    3. • Front vertical up switch terminal K
    • Front vertical down switch terminal J
    • Rear vertical up switch terminal H
    • Rear vertical down switch terminal G
    • Horizontal forward switch terminal D
    • Horizontal rearward switch terminal C
    • Recline forward switch terminal F
    • Recline rearward switch terminal A
    ⇒If not the specified value, replace the seat adjuster switch.
  3. Test for less than 1 ohm between each seat direction signal terminal listed below and the B+ terminal E with the switch in the closed position.
    4. • Front vertical up switch terminal K
    • Front vertical down switch terminal J
    • Rear vertical up switch terminal H
    • Rear vertical down switch terminal G
    • Horizontal forward switch terminal D
    • Horizontal rearward switch terminal C
    • Recline forward switch terminal F
    • Recline rearward switch terminal A
    ⇒If greater than the specified range, replace the seat adjuster switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Power Seat Switch Replacement
    •  Power Seat Adjuster Mechanism Replacement
    •  Control Module References for MSM replacement, programming, and setup.