Chevrolet Silverado / GMC Sierra. Service manual — part 2698

and ground.

Vertical lumbar terminal B

Horizontal lumbar terminal D

If greater than the specified range, test the control circuit for a short to voltage or an
open/high resistance. If circuit tests normal, replace the lumbar switch.

4. Connect a test lamp between affected control circuit terminals listed.

Vertical lumbar terminal A to terminal B

Horizontal lumbarterminal C to terminal D

5. Operate the affected switch in both directions. The test lamp should turn ON when the

switch is pressed in both directions.

If the test lamp remains OFF during either of the commands, test for a short to ground
on either control circuit. If the circuits test normal, replace the lumbar switch.

6. If all circuits test normal, test or replace the lumbar support.

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 control terminal and the B+ terminal with the

switch in the open position.

If less than 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.

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.

If greater than the specified range, replace the seat adjuster switch.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Power Seat Switch Replacement

Front Seat Adjuster Replacement (Power)

Lumbar Switch Replacement

Front Seat Lumbar Support Replacement

2008 Chevrolet Silverado 1500

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

Silverado

Front Seat Recliner Actuator Motor Replacement

POWER SEAT INOPERATIVE (W/MEMORY)

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+

1

1

-

-

B+

2

2

-

-

Front Vertical
Down Switch
Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Front Vertical Up
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Horizontal
Forward Switch
Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Horizontal
Rearward Switch
Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Lumbar Down
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Lumbar Up
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

-

2008 Chevrolet Silverado 1500

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

Silverado

B1815 01, B1820 01

Lumbar Forward
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Lumbar Rearward
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Rear Vertical
Down Switch
Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Rear Vertical Up
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Recline Forward
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Recline Rearward
Switch Signal

2

1

B1735 01, B1740 01,
B1745 01, B1750 01,
B1755 01, B1760 01,

B1815 01, B1820 01

-

Front Vertical
Motor Front
Down Control

B3920 02

1

B3920 01

B2355 5A

Front Vertical
Motor Front Up
Control

B3920 02

1

B3920 01

B2355 5A

Horizontal Motor
Forward Control

B3920 02

1

B3920 01

B2375 5A

Horizontal Motor
Rearward Control

B3920 02

1

B3920 01

B2375 5A

Lumbar
Horizontal Motor
Forward Control

B3920 02

1

B3920 01

B1850 5A

2008 Chevrolet Silverado 1500

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

Silverado

Circuit/System Description

The 8-way power driver seat with memory is controlled by the memory seat module (MSM). The
low current battery supply circuit from the DSM 10A fuse supplies the logic power and reference
voltages to the MSM. The high current battery supply circuit from the DRIVER SEAT 2 25A
circuit breaker supplies the MSM power rail 1 which is used to drive the power seat motors,
adjustable pedals motor, and seat heater elements with heated seats only. The MSM supplies a
battery voltage reference circuit to the seat adjuster and lumbar switches. The switch signal
circuits are referenced from ground within the MSM and when a switch is activated the signal
circuit goes high. Each seat adjuster motor is controlled by the MSM through 2 motor control
circuits. While the seat adjuster motors are in an inactive state the motor control circuits are
closed to ground circuit contacts within the MSM. The MSM operates the seat adjuster motors by
switching one of a motors control circuits to battery voltage. The seat adjuster motors are
bidirectional and the direction of adjuster motor rotation is determined by which of the adjuster
motor control circuits is switched to battery voltage while the other remains grounded.

Lumbar
Horizontal Motor
Rearward Control

B3920 02

1

B3920 01

B1850 5A

Lumbar Vertical
Motor Down
Control

B3920 02

1

B3920 01

B1860 5A

Lumbar Vertical
Motor Up Control

B3920 02

1

B3920 01

B1860 5A

Rear Vertical
Motor Rear Down
Control

B3920 02

1

B3920 01

B2365 5A

Rear Vertical
Motor Rear Up
Control

B3920 02

1

B3920 01

B2365 5A

Recline Motor
Forward Control

B3920 02

1

B3920 01

B1825 5A

Recline Motor
Rearward Control

B3920 02

1

B3920 01

B1825 5A

Ground

-

-

-

-

Ground

-

-

-

-

1. Driver power seat, lumbar, and memory functions inoperative
2. Scan Tool Does Not Communicate with Low Speed GMLAN Device

2008 Chevrolet Silverado 1500

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

Silverado