Chevrolet Silverado / GMC Sierra. Service manual — part 2695

Circuit/System Description

The memory seat module (MSM) controls the seat, lumbar, and adjustable pedal motors via half
bridges that are connected to a common power rail internal to the module. Group 1 includes the
following motors:

Seat front vertical motor

Seat rear vertical motor

Seat horizontal motor

Seat recline motor

Seat lumbar horizontal motor

Seat lumbar vertical motor

Adjustable pedal motor

When a power seat switch is pressed or when a memory recall is requested, each seat or lumbar
motor receives battery voltage and ground from the MSM via the motor control circuits. All seat
and lumbar motors are reversible, so the direction the seat moves depends on which control
circuit voltage is applied and which control circuit the ground is applied. For example, to move
the seat in the forward direction, the module applies voltage to the seat horizontal motor forward
control circuit, and ground to the seat horizontal motor rearward control circuit. When the seat is
operated in the opposite direction, the module reverses the polarity and applies voltage and
ground to the opposite circuits to move the seat in the rearward direction. All seat and lumbar
motors are powered this way.

Conditions for Running the DTC

The MSM must be powered.

Conditions for Setting the DTC

B3920 01

Control

B3920 02

1

B3920 01

-

Driver Seat Lumbar Motor
Rearward Control

B3920 02

1

B3920 01

-

Adjustable Pedal Motor
Forward Down Control

B3920 02

1

B3920 01

-

Adjustable Pedal Motor
Rearward Control

B3920 02

1

B3920 01

-

1. Power seat motor inoperative

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Power Seats - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

The MSM detects a short to battery voltage on a group 1 motor control circuit.

B3920 02

The MSM detects a short to ground on a group 1 motor control circuit.

Action Taken When the DTC Sets

The MSM disables all motors in the group for which the DTC was set.

Conditions for Clearing the DTC

The current DTC clears when the malfunction is no longer present, and the power mode
changes to OFF then back to ACC or RUN.

A history DTC will clear after 50 ignition cycles or with a scan tool using the clear DTCs
function.

Reference Information

Schematic Reference

Driver Seat Schematics

Passenger Seat Schematics

Adjustable Pedal 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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Power Seats - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Control Module References for Scan Tool Information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the MSM.

2. Ignition ON, verify that a test does not illuminate between any of the following motor

control circuits and ground:

Front vertical motor terminal 12

Front vertical motor terminal 13

Rear vertical motor terminal 15

Rear vertical motor terminal 16

Seat horizontal motor terminal 9

Seat horizontal motor terminal 10

If the test lamp illuminates, test the control circuit for a short to voltage.

3. Test for infinite resistance between the following motor control circuits and ground:

Front vertical motor terminal 12

Front vertical motor terminal 13

Rear vertical motor terminal 15

Rear vertical motor terminal 16

Seat horizontal motor terminal 9

Seat horizontal motor terminal 10

If less than infinite resistance, test the motor control circuit for a short to ground.

4. Test for greater resistance values than specified between the following motor control

circuits:

1 ohm for front vertical motor terminal 12 and terminal 13

1 ohm for rear vertical motor terminal 15 and terminal 16

1 ohm for seat horizontal motor terminal 9 and terminal 10

If less than the specified resistance, test the control circuits for a short together or
shorted motor.

5. Ignition OFF, disconnect the harness connector X4 at the MSM.

6. Ignition ON, verify that a test does not illuminate between any of the following motor

control circuits and ground:

Lumbar vertical motor terminal 1

Lumbar vertical motor terminal 2

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Power Seats - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Lumbar horizontal motor terminal 12

Lumbar horizontal motor terminal 13

Seat recline motor terminal 15

Seat recline motor terminal 16

Adjustable pedal motor terminal 9

Adjustable pedal motor terminal 10

If the test lamp illuminates, test the control circuit for a short to voltage.

7. Test for infinite resistance between the following motor control circuits and ground:

Lumbar vertical motor terminal 1

Lumbar vertical motor terminal 2

Lumbar horizontal motor terminal 12

Lumbar horizontal motor terminal 13

Seat recline motor terminal 15

Seat recline motor terminal 16

Adjustable pedal motor terminal 9

Adjustable pedal motor terminal 10

If less than infinite resistance, test the motor control circuit for a short to ground.

8. Test for greater resistance values than specified between the following motor control

circuits:

1 ohm for lumbar horizontal motor terminal 12 and terminal 13

1 ohm for recline motor terminal 15 and terminal 16

If less than the specified resistance, test the control circuits for a short together or
shorted motor.

9. If all circuits test normal, replace the MSM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Front Seat Adjuster Replacement (Power)

Front Seat Recliner Actuator Motor Replacement

Front Seat Lumbar Support Replacement

Brake Pedal Assembly Replacement

Control Module References for the memory seat module replacement, programming and

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Power Seats - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado