Horn Systems: Overview Chevrolet Silverado 2500

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. 2) - Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 4) - The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

Scheme 1

Scheme 2

The numbers below refer to the step numbers on the diagnostic table.

1. 2) - Listen for an audible click when the horn relay operates. Commands both the ON and OFF states. Repeat the commands as necessary.
2. 3) - Tests for voltage at the coil side of the horn relay. The HORN fuse supplies power to the coil side of the horn relay.
3. 4) - Verifies that the body control module (BCM) is providing ground to the horn relay.
4. 5) - Tests if ground is constantly being applied to the horn relay.

Scheme 3

Symptoms - Horns

Important: The following steps must be completed before using the symptom tables.

1. Perform «Diagnostic Starting Point - Horns»(ref-176701-S33121632382005051300000) before using the symptom tables in order to verify that all of the following are true: There are no DTCs set. The body control module (BCM) 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 & Operation»(ref-176701-S40596253562005051300000) .

The numbers below refer to the step numbers on the diagnostic table.

1. 4) - Tests if ground is constantly being applied to the horn relay.
2. 5) - The horn relay control circuit includes the horn switch. The horn switch must be tested for a short to ground when testing the relay control circuit.

The numbers below refer to the step numbers on the diagnostic table.

1. 4) - Verifies that the body control module (BCM) is providing ground to the horn relay.
2. 5) - Tests for voltage at the battery positive voltage terminal of the horn relay coil.
3. 7) - Tests for voltage at the battery positive voltage terminal of the horn relay switch. The HORN fuse supplies power to the battery positive voltage terminal of the horn relay switch.
4. 13) - The horns need maximum current flow to operate properly. A high resistance (greater than 0.5ohms) in the horn control circuit or the horn ground circuit could cause operating problems with the horns. Inspect the circuits for faults that would restrict current flow.
5. 15) - The horn relay control of circuit includes the horn switch. The horn switch must be tested for a high resistance, an open or a short to voltage when testing the relay control circuit.

Scheme 4

Scheme 5

The number below refers to the step number on the diagnostic table.

1. 9) - The horns need maximum current flow to operate properly. A high resistance - greater than 0.5ohms - in the horn control circuit or the horn ground circuit could cause operating problems with the horns. Inspect the circuits for faults that would restrict current flow.

Scheme 6

Scheme 7

Scheme 8

1. Raise the hood.
2. Remove the headlamp assembly. Refer to «HEADLAMP ASSEMBLY OR HEADLAMP BULB REPLACEMENT»(ref-176693-S17794972152005051000000) .
3. Remove the park/turn signal lamp assembly. Refer to «PARK/TURN SIGNAL LAMP REPLACEMENT»(ref-176693-S39976901632005051000000) .
4. Disconnect the horn electrical connector.
5. Remove the horn bolt. Reposition the park/turn signal lamp wiring harness for additional clearance.
6. Remove the horn (2) from the radiator support (1). Left side and right side horn assemblies are shown.

System Description

The horn system consists of the following components

1. Horn fuse
2. Horn relay
3. Horn switch
4. Horn(s)
5. Body Control Module (BCM)

System Operation

The vehicle horns are activated under the following conditions

1. The horn switch is depressed.
2. The body control module (BCM) commands the horns on. The BCM commands the horns on under either of the following conditions: When the content theft deterrent system detects a vehicle intrusion. For further information, refer to «THEFT SYSTEMS DESCRIPTION & OPERATION»(ref-176706-S32879241292005051200000) . When the panic button is depressed on the remote control door lock transmitter. For further information, refer to «KEYLESS ENTRY SYSTEM DESCRIPTION & OPERATION»(ref-176703-S15043449712005051200000) . When the OnStar® system is used to sound the horns, if equipped. For further information, refer to «ONSTAR® DESCRIPTION & OPERATION»(ref-176696-S32934814342005051100000) . When the keyless entry system is used to lock the vehicle, a horn chirp may sound to notify the driver that the vehicle has been locked. The notification feature may be enabled or disabled through personalization. For further information, refer to «KEYLESS ENTRY SYSTEM DESCRIPTION & OPERATION»(ref-176703-S15043449712005051200000) .

Circuit Operation

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