GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Cobalt 🢒 Body 🢒 Horns 🢒 Horns Inoperative

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Horn Relay Control

1

2

B2750 01

--

Horn Control

2

2

1

--

Horn Switch Ground

--

2

2

--

Horn Ground

--

2

2

--

1. Horn Always On

2. Horn Inoperative

Circuit/System Description

Battery positive voltage is applied at all times to the horn relay coil and the horn relay switch. Pressing the horn button applies ground to the horn relay control circuit. The body control module (BCM) also has the capability to ground the horn relay control circuit as the circuit passes through the BCM. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn through the horn control circuit. The horn sounds as long as ground is applied to the horn relay control circuit.

Diagnostic Aids

When 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.
    • Debris in the joint where the horns attach to the vehicle.
    • Debris in direct contact with the horn
    • Vehicle components vibrating while the horn is sounding

Reference Information

Schematic Reference

Horn Schematics

Connector End View Reference

Horn Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. Ignition ON, press and release the steering wheel horn pad. The horn should sound and emit a clear and even tone only when the horn pad is pressed.
    2. ⇒If the horn does not sound when the horn pad is pressed, refer to Horn Malfunction - Horn Pad.
    ⇒If the sound emitted from the horn is not clear and even, refer to Horn - Poor Tone.
  2. Command the Horn ON and OFF with the scan tool. The horn should turn ON and OFF when changing between the commanded states.
    3. ⇒If the horn does not turn ON and OFF when changing between the commanded states, replace the BCM.

Circuit/System Testing

Horn Malfunction - Horn Pad

  1. Ignition OFF, disconnect the harness connector at the horn switch.
  2. Test for less than 1.0 ohm between the ground circuit terminal 2 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the harness connector at the horn switch.
  4. Disconnect the C2 harness connector at the underhood fuse block.
  5. Connect a test lamp between the control circuit terminal B6 and B+.
  6. Press and release the horn pad. The test lamp should turn ON and OFF when changing between the commanded states.
    7. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the horn switch.
    ⇒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 horn switch.
  7. Connect the C2 harness connector at the underhood fuse block.
  8. Disconnect the harness connector at the horn.
  9. Test for less than 1.0 ohm between the ground circuit terminal A and ground.
    10. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  10. Connect a test lamp between the control circuit terminal B and ground.
  11. Press and release the horn pad. The test lamp should turn ON and OFF when changing between the commanded states.
    12. ⇒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, replace the underhood fuse block.
  12. If all circuits test normal, test or replace the horn.

Horn - Poor Tone

  1. Ignition OFF, disconnect the harness connector at the horn.
  2. Test for less than 1.0 ohm between the ground circuit terminal A and ground.
    3. ⇒If greater than the specified range, test the ground circuit for a high resistance.
  3. Disconnect the C3 harness connector at the underhood fuse block.
  4. Test for less than 1.0 ohm between the control circuit terminal E3 and the control circuit terminal B at the horn.
    5. ⇒If greater than the specified range, test the control circuit for a high resistance.
  5. If all circuits test normal, test or replace the horn.

Component Testing
  1. Ignition OFF, disconnect the harness connector at the horn.
  2. Install a 10A fused jumper wire between the control terminal A and 12 volts. Install a jumper wire between the ground terminal B and ground. Verify the horn emits a clear and even tone.
    3. ⇒If the sound emitted is not clear and even, replace the horn.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Horn Replacement
    •  Underhood Electrical Center or Junction Block Bracket Replacement
    •  Control Module References for BCM replacement, setup, and programming