Chevrolet Silverado / GMC Sierra. Service manual — part 2756

DTC B2508 OR B2509

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.

DTC Descriptors

DTC B2508 01

Seat Heater Relay Circuit Shorted to Battery or Open

DTC B2508 02

Seat Heater Relay Circuit Shorted to Ground

Diagnostic Fault Information

Circuit/System Description

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Left Heated Seat Back
Element Supply Voltage

B2508 02

B1935 0C

B1935 0D

B2508 01

-

Left Heated Seat Cushion
Element Supply Voltage

B2508 02

B2425 0C

B2425 0D

B2508 01

-

Left Heated Seat Back
Element Control

B2508 02

B1935 0C
B1935 0D

B2508 01

-

Left Heated Seat Cushion
Element Control

B2508 02

B2425 0C

B2425 0D

B2508 01

-

Right Heated Seat Back
Element Supply Voltage

B2508 02

B2180 0C

B2180 0D

B2508 01

-

Right Heated Seat Cushion
Element Supply Voltage

B2508 02

B2430 0C

B2430 0D

B2508 01

-

Right Heated Seat Back
Element Control

B2508 02

B2180 0C
B2180 0D

B2508 01

-

Right Heated Seat Cushion
Element Control

B2508 02

B2430 0C
B2430 0D

B2508 01

-

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Seat Heating and Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

The front seat heating elements are controlled by a common high current relay internal to the
Memory Seat Module (MSM) and on the low side by individual element control circuits. The
module connects the heated seat heater element supply voltage circuits to a common reference
point. This reference point is biased to approximately 2.0 volts. Before the module will allow
heated seat operation, it checks to see if the heating element supply voltage circuits and control
circuits are shorted to ground or battery voltage. Once the module verifies that it is not closing
into a shorted heating element, it allows heated seat operation. After which it continues to
monitor for a shorted circuit.

Conditions for Running the DTC

The MSM must be powered.

Conditions for Setting the DTC

B2508 02

Before the heated seats are activated, the MSM detects a short to ground on the seat heating
element supply voltage circuit or control circuit.

B2508 01

Before the heated seats are activated, the MSM detects a short to battery voltage on the seat
heating element supply voltage circuit or control circuit.

Action Taken When the DTC Sets

The heated seat function for both seats will be disabled.

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.

The history DTC will clear after 50 consecutive fault-free ignition cycles have occurred.

Reference Information

Schematic Reference

Heated/Cooled Seat Schematics

Connector End View Reference

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Seat Heating and Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Component Connector End Views

Description and Operation

Heated 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 Testing

1. Ignition OFF, disconnect the X1, X4 harness connectors at the MSM.

2. Test for infinite resistance between the driver seat heating element supply voltage circuit

terminal 14 X1 and ground.

If less than the specified range, test the supply voltage circuit and the seat cushion and
seat back heating element control circuits for a short to ground.

3. Ignition ON, verify that a test lamp does not illuminate between the supply voltage circuit

terminal 14 X1 and ground.

If the test lamp illuminates, test the supply voltage circuit and the seat cushion and seat
back heating element control circuits for a short to voltage.

4. Test for infinite resistance between the passenger seat heating element supply voltage circuit

terminal 6 X1 and ground.

If less than the specified range, test the supply voltage circuit and the seat cushion and
seat back heating element control circuits for a short to ground.

5. Ignition ON, verify that a test lamp does not illuminate between the supply voltage circuit

terminal 6 X1 and ground.

If the test lamp illuminates, test the supply voltage circuit and the seat cushion and seat
back heating element control circuits for a short to voltage.

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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Seat Heating and Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Driver Seat and Passenger Seat Back Cushion Heater Replacement

Driver Seat and Passenger Seat Cushion Heater Replacement

Control Module References for the MSM replacement, setup, and programming

SYMPTOMS - SEAT HEATING AND COOLING

1. Perform the Diagnostic System Check - Vehicle before using the Symptom Tables in

order to verify that all of the following are true:

There are no DTCs set.

The control modules can communicate via the serial data link.

2. Review the system operation in order to familiarize yourself with the system functions.

Refer to Heated Seats Description and Operation.

Visual/Physical Inspection

Inspect for aftermarket devices which could affect the operation of the system. Refer to
Checking Aftermarket Accessories .

Inspect the easily accessible or visible system components for obvious damage or conditions
which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to Heated Seat Inoperative in order to diagnose the symptom.

HEATED SEAT INOPERATIVE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

IMPORTANT: The following steps must be completed before using the symptom

tables.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Seat Heating and Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado