Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
- 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.
- 3: The symptoms list in Symptoms will determine the correct diagnostic procedure to use.
- 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. At this point you have determined all DTCs applicable to the horn system. Refer to «Symptoms - Horns»(ref-190293-S08600780132005091400000) for further horn system diagnosis. Any other codes displayed from the listed modules do not apply to horns and should be diagnosed in the applicable section.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to SCAN TOOL DOES NOT POWER UP in Data Link Communications |
| 2 | Turn ON the ignition, with the engine OFF. Attempt to establish communication with the body control module (BCM). Does the scan tool communicate with the BCM? | Go to Step 3 | Go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE (W/O IMMOBILIZER) in Data Link Communications |
| 3 | Select the BCM display DTCs function on the scan tool. Does the scan tool display any DTCs? | Go to Step 4 | Go to Symptoms - Horns |
| 4 | Does the scan tool display any DTCs which begin with a "U"? | Go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE (W/O IMMOBILIZER) in Data Link Communications | Go to Step 5 |
| 5 | Does the scan tool display DTC B1000? | Go to DIAGNOSTIC TROUBLE CODE (DTC) LIST in Body Control System | Go to Symptoms - Horns |
Diagnostic System Check - Horns
The numbers below refer to the step numbers on the diagnostic table.
- 4: Tests if ground is constantly being applied to the horn relay.
- 5: The horn relay control circuit includes the horn switch. The horn switch is part of the inflatable restraint steering wheel module. The horn switch must be tested for a short to ground when testing the relay control circuit.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Horns? | Go to Step 2 | Go to Diagnostic System Check - Horns |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the body control module (BCM) Horn Output ON and OFF. Are the horns on at all times? | Go to Step 3 | Go to TESTING FOR INTERMITTENT CONDITIONS AND POOR in Wiring Systems |
| 3 | Turn OFF the ignition. Disconnect the horn relay. Are the horns on at all times? | Go to Step 8 | Go to Step 4 |
| 4 | Connect a test lamp between the battery positive voltage circuit of the horn relay coil and the horn relay control circuit. Does the test lamp illuminate? | Go to Step 5 | Go to Step 6 |
| 5 | IMPORTANT: The horn switch is part of the inflatable restraint steering wheel module. Refer to AIR BAG MODULES in SIR. To disable the SIR system refer to DISABLING & ACTIVATING AIR BAG SYSTEM in SIR.Test the horn relay control circuit for a short to ground. The horn relay control circuit includes the horn switch. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems.Did you find and correct the condition? | Go to Step 11 | Go to Step 7 |
| 6 | Inspect for poor connections at the horn relay. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and to CONNECTOR REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 7 | Inspect for poor connections at the harness connector of the BCM. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONDITIONS and to CONNECTOR REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
| 8 | Repair the short to voltage in the horn control circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 11 | |
| 9 | Replace the horn relay. Refer to Horn Relay Replacement in Horns. Did you complete the replacement? | Go to Step 11 | |
| 10 | IMPORTANT: Perform the BCM setup procedure when replacing the BCM. Replace the BCM. Refer to BODY CONTROL MODULE REPLACEMENT in Body Control Systems.Did you complete the replacement? | Go to Step 11 | |
| 11 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1 |
| IMPORTANT |
|---|
| The horn switch is part of the inflatable restraint steering wheel module. Refer to AIR BAG MODULES in SIR. |
| IMPORTANT |
|---|
| Perform the BCM setup procedure when replacing the BCM. |
Horns Always On
The numbers below refer to the step numbers on the diagnostic table.
- 4: Verifies that the body control module (BCM) is providing ground to the horn relay.
- 5: Tests for voltage at the battery positive voltage terminal of the horn relay coil.
- 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.
- 15: The horns need maximum current flow to operate properly. A high resistance (greater than 0.5 ohm) in the horn control circuit or the horn ground circuit could cause operating problems with the horns. Check the circuits for faults that would restrict current flow.
- 17: The horn relay control circuit includes the horn switch. The horn switch is part of the inflatable restraint steering wheel module. The horn switch must be tested for a high resistance, an open or a short to voltage when testing the relay control circuit.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Horns? | Go to Step 2 | Go to Diagnostic System Check - Horns |
| 2 | Depress the horn switch. Do the horns operate? | Go to Step 3 | Go to Step 5 |
| 3 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the body control module (BCM) Horn Output ON and OFF. Do the horns operate? | Go to TESTING FOR INTERMITTENT CONDITIONS AND POOR in Wiring Systems | Go to Step 4 |
| 4 | Test the BCM portion of the horn relay control circuit for a high resistance or an open. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 24 | Go to Step 13 |
| 5 | Turn OFF the ignition. Disconnect the horn relay. Connect a test lamp between the battery positive voltage circuit of the horn relay coil and a good ground. Does the test lamp illuminate? | Go to Step 6 | Go to Step 16 |
| 6 | Connect a test lamp between the battery positive voltage circuit of the horn relay coil and the horn relay control circuit. Depress and hold the horn switch. Does the test lamp illuminate? | Go to Step 7 | Go to Step 17 |
| 7 | Connect a test lamp between the battery positive voltage circuit of the horn relay switch and a good ground. Does the test lamp illuminate? | Go to Step 8 | Go to Step 18 |
| 8 | Momentarily connect a 15-amp fused jumper wire between the battery positive voltage circuit of the horn relay switch and the horn control circuit. Do the horns operate? | Go to Step 14 | Go to Step 9 |
| 9 | Reconnect the horn relay. Disconnect the horn connector. Connect a test lamp between the horn control circuit and a good ground. Depress and hold the horn switch. Does the test lamp illuminate? | Go to Step 10 | Go to Step 19 |
| 10 | Connect a test lamp between the horn control circuit and the horn ground circuit. Depress and hold the horn switch. Does the test lamp illuminate? | Go to Step 11 | Go to Step 20 |
| 11 | Inspect for poor connections at the harness connector of the horn. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and to CONNECTOR REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 24 | Go to Step 12 |
| 12 | Connect a 15-amp fused jumper wire between the positive battery terminal and the control terminal of the horn. Connect another jumper wire between the negative battery terminal and the ground terminal of the horn. Do the horns operate? | Go to Step 15 | Go to Step 23 |
| 13 | Inspect for poor connections at the harness connector of the BCM. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and to CONNECTOR REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 24 | Go to Step 21 |
| 14 | Inspect for poor connections at the horn relay. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and to CONNECTOR REPAIRS in Wiring Systems. Did you find and correct the condition? | Go to Step 24 | Go to Step 22 |
| 15 | Repair the high resistance in the horn control circuit or the horn ground circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 24 | |
| 16 | Repair the open or high resistance in the battery positive voltage circuit of the horn relay coil. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 24 | |
| 17 | IMPORTANT: The horn switch is part of the inflatable restraint steering wheel module. Refer to AIR BAG MODULES in SIR. To disable the SIR system refer to DISABLING & ACTIVATING AIR BAG SYSTEM in SIR.Repair the open or short to voltage in the horn relay control circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems.Did you complete the repair? | Go to Step 24 | |
| 18 | Repair the open or high resistance in the battery positive voltage circuit of the horn relay switch. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 24 | |
| 19 | Repair the open or high resistance in the horn control circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 24 | |
| 20 | Repair the open or high resistance in the horn ground circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 24 | |
| 21 | IMPORTANT: Perform the BCM procedure when replacing the BCM. Replace the BCM. Refer to BODY CONTROL MODULE REPLACEMENT in Body Control Systems.Did you complete the repair? | Go to Step 24 | |
| 22 | Replace the horn relay. Refer to Horn Relay Replacement in Horn. Did you complete the replacement? | Go to Step 24 | |
| 23 | Replace the horns. Refer to Horn Replacement in Horn. Did you complete the replacement? | Go to Step 24 | |
| 24 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1 |
| IMPORTANT |
|---|
| The horn switch is part of the inflatable restraint steering wheel module. Refer to AIR BAG MODULES in SIR. |
| IMPORTANT |
|---|
| Perform the BCM procedure when replacing the BCM. |
Horns Inoperative
Horns - Poor Tone
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Horns Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Horns |
| 2 | Depress the horn switch. Do the horns have a harsh tone or buzzing? | Go to Step 3 | Go to Symptoms - Horns |
| 3 | Test the horn mounting hardware for adequate torque. The hardware should be tightened to 10 N.m (7 lb ft). Inspect the horns for debris in the joint where the horns attach to the vehicle. Did you find and correct the condition? | Go to Step 7 | Go to Step 4 |
| 4 | Disconnect the horn connector. Connect a 15 amp fuse jumper wire between the positive battery terminal and the control terminal of the horn. Connect another jumper wire between the negative battery terminal and the ground terminal of the horn. Do the horns have a harsh tone or buzzing? | Go to Step 6 | Go to Step 5 |
| 5 | Repair the high resistance in the horn control circuit or the horn ground circuit. Refer to CIRCUIT TESTING and to WIRING REPAIRS in Wiring Systems. Did you complete the repair? | Go to Step 7 | |
| 6 | Replace the horns. Refer to Horn Replacement in Horn. Did you complete the replacement? | Go to Step 7 | |
| 7 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1 |
Horns - Poor Tone
System Description
The horn system consists of the following components
- The BATTERY fuse
- The HORN fuse
- The horn relay
- The horn switch
- The horns
- The body control module (BCM)
System Operation
The vehicle horn system is activated under the following conditions
- The horn switch is depressed.
- The body control module (BCM) commands the horns on. The BCM commands the horns on under any of the following conditions: When the content theft deterrent system detects a vehicle intrusion. For further information refer to «CONTENT THEFT DETERRENT (CTD) DESCRIPTION AND OPERATION»(ref-189237-S41375011782005090800000) in Theft Deterrent. When the panic button is depressed on the remote control door lock transmitter. For further information refer to «KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION»(ref-190235-S37896528502005091300000) in Keyless Entry. When the OnStar(R) system is used to sound the horns (if equipped.) For further information refer to «ONSTAR DESCRIPTION AND OPERATION»(ref-188882-S05275448492005090900000) . When the lock button on the keyless entry transmitter is pressed twice within 5 seconds, a horn chirp will sound to notify the driver that the vehicle has been locked. For further information refer to «KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION»(ref-190235-S37896528502005091300000) in Keyless Entry.
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 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 horns through the horn control circuit. The horns sound as long as ground is applied to the horn relay control circuit.