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Chevrolet Silverado / GMC Sierra. 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
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