Chevrolet Silverado / GMC Sierra. Manual

Visual/Physical Inspection

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

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

Perform the following if a horn buzzes or has a harsh tone.

Inspect for debris in the joint where the horn fastens to the vehicle.

Test the torque of the horn mounting hardware. The horn mounting hardware should be
tightened to a torque of 10 N.m (7 lb ft).

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 a symptom diagnostic procedure Horns Malfunction in order to diagnose the symptom.

HORNS MALFUNCTION

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

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 Horns System
Description and Operation.

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

2008 Chevrolet Silverado 1500

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

Circuit/System Description

Battery positive voltage is applied at all times to the horn relay coil and horn relay switch.
Pressing the horn switch applies ground to the horn relay control circuit. The body control
module (BCM) also may apply ground to the horn relay control circuit. When the horn relay
control circuit is grounded, the horn relay is energized and battery positive voltage is applied to
the horn via the horn control circuit. The horn will sound as long as ground is applied to the horn
relay control circuit.

Diagnostic Aids

If diagnosing a Horn - Poor Tone condition, inspect the following:

Debris or water in the horn assembly.

Proper horn mounting hardware torque. Refer to Fastener Tightening Specifications.

Debris in the joint where the horns attach to the vehicle.

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

Circuit Testing

Horn Relay Control

B2750 00

Horn Control

Horn Switch Ground

Horn Ground

1. Horn Always On
2. Horn Inoperative

2008 Chevrolet Silverado 1500

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

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition OFF, connect a test lamp between the HORN fuse test point and ground.

2. Press and release the horn switch. The test lamp should turn ON and OFF when changing

between the commanded states.

If the test lamp does not illuminate or remains illuminated at all times, refer to Horn
Switch Circuit Test below.

3. Ignition ON, 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 does not illuminate, test the control circuit terminal 18 at the BCM for
a short to voltage or an open/high resistance. If the circuit tests normal, replace the
BCM.

4. Connect a 10A fused jumper wire between the HORN fused test point and B+. The horns

should sound and emit a clear and even tone.

If the horn does not sound, refer to Horn Circuit Test below.

If the sound emitted is not clear and even, refer to Horn - Poor Tone below.

Circuit/System Testing

Horn Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the horn switch.

2. Test for less than 1 ohm between the ground circuit terminal B and ground.

If greater than the specified range, test the ground circuit for and open/high resistance.

3. Connect the harness connector at the horn switch.

4. Disconnect the X4 harness connector at the underhood fuse block.

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

6. Press and release the horn switch. The test lamp should turn ON and OFF when changing

between the commanded states.

2008 Chevrolet Silverado 1500

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

If the test lamp is always ON, test the control circuit for a short to ground or a sticking
horn switch. If the circuit tests normal, replace the BCM.

If the test lamp is always OFF, test the control circuit for a short to voltage, an open
high resistance, or a horn switch which is not closing.

7. Ignition OFF, connect the harness connector at the underhood fuse block. Disconnect the

harness connector at the appropriate horn.

8. Verify that a test lamp does not illuminate between the control circuit terminal B and

ground.

If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit
tests normal, replace the underhood fuse block.

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

Horn Circuit Test

1. Ignition OFF, disconnect the harness connector at the appropriate horn.

2. Test for less than 1 ohm between the ground circuit terminal A and ground.

If greater than the specified range, test the ground circuit for and open/high resistance.

3. Connect a test lamp between the control circuit terminal B and ground.

4. Press and release the horn switch. The test lamp should turn ON and OFF when changing

between the commanded states.

If the test lamp is always ON, test the control circuit for a short to voltage. If the
circuit tests normal, replace the underhood fuse block.

If the test lamp is always OFF and the circuit fuse is good, test the control circuit for
an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a
short to ground. If the circuit tests normal, test or replace the horn.

5. If all circuit test normal, test or replace the horn.

Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the appropriate horn.

2. Test for less than 1 ohm between the horn ground circuit terminal A and ground.

If greater than the specified range, test the ground circuit for a high resistance.

3. Disconnect the X1 harness connector at the underhood fuse block.

4. Test for less than 1 ohm between the control circuit terminal E5 at the underhood fuse block

and the control circuit terminal B at the horn.

2008 Chevrolet Silverado 1500

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

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