Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 2: Listen for an audible click when the horn relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
- 3: This step tests for voltage at the coil side of the horn relay. The HORN fuse supplies power to the coil side of the horn relay.
- 4: This step verifies that the BCM is providing ground to the horn relay.
- 5: This step tests if ground is constantly being applied to the horn relay.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Horn Schematics | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the horn relay ON and OFF. Does the horn relay turn ON and OFF with each command? | Go to Diagnostic Aids | Go to Step 3 |
| 3 | Turn OFF the ignition. Disconnect the horn relay. Turn ON the ignition, with the engine OFF. 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 4 | Go to Step 10 |
| 4 | Connect a test lamp between the control circuit of the horn relay and the battery positive voltage circuit of the horn relay coil. With a scan tool, command the horn relay ON and OFF. Does the test lamp turn ON and OFF with each command? | Go to Step 8 | Go to Step 5 |
| 5 | Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 6 |
| 6 | Test the control circuit of the horn relay for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
| 7 | Test the control circuit of the horn relay for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
| 8 | Inspect for poor connections at the horn relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
| 9 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
| 10 | Repair the battery positive voltage circuit of the horn relay coil. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 13 | |
| 11 | Replace the horn relay. Did you complete the replacement? | Go to Step 13 | |
| 12 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | |
| 13 | Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. Does the DTC reset? | Go to Step 2 | System OK |
DTC B2752
Symptoms - Horns
| IMPORTANT | The following steps must be completed before using the symptom tables. |
- Perform «Diagnostic System Check - Vehicle»(ref-277883-S07139257572008012100000) , 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.
- Review the system operation in order to familiarize yourself with the system functions. Refer to «Horns System Description and Operation»(ref-277876-S19909749522008012100000) .
The numbers below refer to the step numbers on the diagnostic table.
- 4: This step tests if ground is constantly being applied to the horn relay.
- 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.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 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 Connections |
| 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 Inflatable Restraint Steering Wheel Module Replacement . To disable the SIR system, refer to SIR Disabling and Enabling . 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 Wiring Repairs . 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 Connector Repairs . Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 7 | Inspect for poor connections at the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . 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 Wiring Repairs . Did you complete the repair? | Go to Step 11 | |
| 9 | Replace the horn relay. Refer to Relay Replacement (Attached to Wire Harness) or Relay Replacement (Within an Electrical Center) . Did you complete the replacement? | Go to Step 11 | |
| 10 | Replace the BCM. Refer to Control Module References . Did you complete the replacement? | Go to Step 11 | |
| 11 | Operate the horn. 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 Inflatable Restraint Steering Wheel Module Replacement . |
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.
- 13: The horns need maximum current flow to operate properly. A high resistance, greater than 0.5 ohms, 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.
- 15: The horn relay control 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.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 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 Connections | 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 Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | Go to Step 11 |
| 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 14 |
| 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 15 |
| 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 16 |
| 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 12 | Go to Step 9 |
| 9 | Reconnect the horn relay. Disconnect either 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 17 |
| 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 13 | Go to Step 18 |
| 11 | Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 21 | Go to Step 19 |
| 12 | Inspect for poor connections at the horn relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 21 | Go to Step 20 |
| 13 | Repair the high resistance in the horn control circuit or the horn ground circuit. Also, though unlikely, it is possible that both horns are defective. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 14 | Repair the open or high resistance in the battery positive voltage circuit of the horn relay coil. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 15 | Repair the open or short to voltage in the horn relay control circuit. The horn relay control circuit includes the horn switch. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 16 | Repair the open or high resistance in the battery positive voltage circuit of the horn relay switch. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 17 | Repair the open or high resistance in the horn control circuit. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 18 | Repair the open or high resistance in the horn ground circuit. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 21 | |
| 19 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 21 | |
| 20 | Replace the horn relay. Did you complete the replacement? | Go to Step 21 | |
| 21 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1 |
Horns Inoperative
The number below refers to the step number on the diagnostic table.
- 9: 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. Inspect the circuits for faults that would restrict current flow.
| Step | Action | Yes | No |
|---|---|---|---|
| DEFINITION: This diagnostic procedure is for use with systems that have multiple horns in which one of the horns is inoperative. | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Depress the horn switch. Do all of the horns operate? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
| 3 | Disconnect the inoperative horn. 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 4 | Go to Step 7 |
| 4 | 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 5 | Go to Step 8 |
| 5 | Inspect for poor connections at the inoperative horn. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 11 | Go to Step 6 |
| 6 | 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. Does the horn sound? | Go to Step 9 | Go to Step 10 |
| 7 | Repair the open or poor connection in the horn control circuit. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 11 | |
| 8 | Repair the open or poor connection in the horn ground circuit. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 11 | |
| 9 | Repair the high resistance in the horn control circuit or the horn ground circuit of the horn. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 11 | |
| 10 | Replace the inoperative horn. Refer to Horn Replacement - Left Side and Horn Replacement - Right Side . Did you complete the replacement? | Go to Step 11 | |
| 11 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1 |
Horns Inoperative - One Horn
Horns - Poor Tone
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 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. Refer to Fastener Tightening Specifications . 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 | 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 Wiring Repairs . Did you complete the repair? | Go to Step 7 | |
| 6 | Replace the horns. Refer to Horn Replacement - Left Side and Horn Replacement - Right Side . 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
- Horn fuse
- Horn relay
- Horn switch
- Horn(s)
- Body Control Module (BCM)
System Operation
The vehicle horns are 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 either 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-277887-S37698719072008012100000) . 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-277860-S10182100902008012100000) . When the OnStar® system is used to sound the horns, if equipped. For further information, refer to «OnStar Description and Operation»(ref-277845-S30034518272008012100000) . 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 and Operation»(ref-277860-S10182100902008012100000) .
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.