Chevrolet Silverado / GMC Sierra. Service manual — part 2293

2008 ACCESSORIES & EQUIPMENT

Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

SPECIFICATIONS

FASTENER TIGHTENING SPECIFICATIONS

SCHEMATIC AND ROUTING DIAGRAMS

HORN SCHEMATICS

Fig. 1: Horn Schematic
Courtesy of GENERAL MOTORS CORP.

DIAGNOSTIC INFORMATION AND PROCEDURES

Application

Specification

Metric

English

Horn Bolt

9 N.m

80 lb in

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

DIAGNOSTIC STARTING POINT - HORNS

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic
System Check will provide the following information:

The identification of the control modules which command the system

The ability of the control modules to communicate through the serial data circuit

The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the
system and where the procedure is located.

DTC B2750

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 Descriptor

DTC B2750 00

Horn Relay Coil Circuit

Diagnostic Fault Information

DTC

Description

DTC B2750

B2750 00: Horn Relay Coil Circuit

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Horn Relay Control

B2750 00

B2750 00

B2750 00

-

Horn Control

2

2

1

-

Horn Switch Ground

-

2

2

-

Horn Ground

-

2

2

-

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Circuit/System Description

The body control module (BCM) controls the horn relay by grounding the control circuit of the
horn relay coil energizing the relay. When the horn relay is energized, the horn relay contacts
close applying voltage through the horn fuse and the horn control circuit to the horns.

Conditions for Running the DTC

When the output is actively being requested by the BCM.

Conditions for Setting the DTC

The BCM detects a short to ground, open or short to battery in the horn relay control circuit for
approximately 125 milliseconds.

Action Taken When the DTC Sets

The BCM disables the output to the horn relay until the next ignition cycle.

Conditions for Clearing the DTC

The DTC clears when the fault is no longer detected.

The current DTC will become history when the request for the output is removed.

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

Reference Information

Schematic Reference

Horn Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

1. Horn Always On
2. Horn Inoperative

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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

Command the horn ON and OFF with the scan tool. The horn should turn ON and OFF when
changing between the commanded states.

Circuit/System Testing

1. Ignition OFF, disconnect the X4 harness connector at the underhood fuse block.

2. Connect a test lamp between the control circuit terminal G1 and B+.

3. Command the horn ON and OFF with a scan tool. The test lamp should turn ON and OFF

when changing between the commanded states.

If the test lamp is always OFF, test the control circuit for a short to voltage or an
open/high resistance. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, replace the underhood fuse block.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Underhood Electrical Center or Junction Block Bracket Replacement

Control Module References for BCM replacement, setup and programming

SYMPTOMS - HORNS

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

tables:

1. Perform Diagnostic System Check - Vehicle , before using

the symptom tables in order to verify that all of the following
are true:

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Horns - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado