For 1990-2009 cars

### Test Description

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

1. Tests for voltage at the battery positive voltage terminal of the horn relay coil.

2. 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.

3. 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.

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 Testing for Intermittent Conditions and Poor Connections | Go to Step 3
3 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, command the horn relay ON and OFF.

Do the horns turn ON and OFF with each command?

Go to Step 11

Go to Step 4

4 |

1. Disconnect the horn relay.
2. 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 5

Go to Step 15

5 |

1. Connect a test lamp between the battery positive voltage circuit of the horn relay coil and the horn relay control circuit.
2. Depress and hold the horn switch.

Does the test lamp illuminate?

Go to Step 6

Go to Step 12

6 | 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 7 | Go to Step 16
7 | 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 10 | Go to Step 8
8 |

1. Reconnect the horn relay.
2. Disconnect the horn connector.
3. Connect a test lamp between the horn control circuit and a good ground.
4. Depress and hold the horn switch.

Does the test lamp illuminate?

Go to Step 9

Go to Step 17

9 |

1. Connect a test lamp between the horn control circuit and the horn ground circuit.
2. Depress and hold the horn switch.

Does the test lamp illuminate?

Go to Step 13

Go to Step 18

10 | 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 22 | Go to Step 19
11 | Test the horn switch signal for a short to voltage or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 22 | Go to Step 21
12 | Test the control circuit of the horn relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 22 | Go to Step 21
13 |

1. Connect a 15-amp fused jumper wire between the positive battery terminal and the control terminal of the horn.
2. Momentarily connect another jumper wire between the negative battery terminal and the ground terminal of the horn.

Does the horn sound?

Go to Step 14

Go to Step 20

14 | Repair the high resistance in the horn control circuit or the horn ground. A resistance as low as 0.5 ohms could cause operating problems with the horns. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | Go to Step 22 | --
15 | 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 22 | --
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 22 | --
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 22 | --
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 22 | --
19 | Replace the horn relay. Refer to Relay Replacement . Did you complete the replacement? | Go to Step 22 | --
20 | Replace the horn assembly. Refer to Horn Replacement . Did you complete the replacement? | Go to Step 22 | --
21 | Replace the body control module (BCM). Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 22 | --
22 | Operate the horns. Do the horns operate properly? | System OK | Go to Step 1