For 1990-2009 cars

### Test Description

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

1. Verify if the DIM provides ground for the horn relay.

2. Test the voltage at the horn relay coil battery positive voltage terminal.

3. Test the voltage at the horn relay switch battery positive voltage terminal. Seat breaker provides power to the horn relay switch battery positive voltage terminal.

4. The horn requires the highest current while sounding. If the resistance in the horn control circuit or ground circuit is higher than 0.5 ohm, malfunction may occur. Inspect the circuit for current troubles.

5. The horn relay control circuit includes horn slip ring and horn switch. While testing the relay control circuit, test if the horn slip ring and button has high resistance or is open or short to voltage.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Press the horn switch. Does the horn sound? | Go to Step 3 | Go to Step 5
3 |

1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Use a scan tool to command the BCM horn output ON/OFF.

Does the horn sound?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 4

4 | Test if the DIM components in the horn relay control circuit has a high resistance or is open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | Go to Step 11
5 |

1. Turn OFF the ignition.
2. Disconnect the horn relay.
3. Connect a test lamp at the battery positive voltage circuit of the horn relay coil and good ground.

Does the test light illuminate?

Go to Step 6

Go to Step 14

6 |

1. Connect a test lamp at the battery positive voltage circuit of the horn relay coil and the control circuit of the horn relay.
2. Press and hold the horn button.

Does the test light illuminate?

Go to Step 7

Go to Step 15

7 | Connect a test lamp at the battery positive voltage circuit of the horn relay switch and good ground. Does the test light illuminate? | Go to Step 8 | Go to Step 16
8 | Connect a 15A jumper at the battery positive voltage circuit of the horn relay switch and the control circuit of the horn relay. Does the horn sound? | Go to Step 10 | Go to Step 17
9 |

1. Re-connect the horn relay.
2. Disconnect any one of the horn connectors.
3. Connect a test lamp between the horn control circuit and the good ground.
4. Press and hold the horn button.

Does the test light illuminate?

Go to Step 10

Go to Step 17

10 |

1. Connect a test lamp between the horn control circuit and the horn ground circuit.
2. Press and hold the horn button.

Does the test light illuminate?

Go to Step 13

Go to Step 18

11 | Check for poor connections at the harness connector of the DIM. Refer to Testing for Intermittent Conditions and Poor Connections . Did you find and correct the condition? | Go to Step 21 | Go to Step 19
12 | Inspect for poor connection of the horn relay. Refer to Testing for Intermittent Conditions and Poor Connections . 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 and horn ground circuit. resistance as low as 0.5 ohm can cause trouble to the horn. Though rarely possible, both horns may fail at the same time . Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

--

14 | Repair the open circuit or high resistance at the horn relay coil battery positive voltage circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | --
15 | Repair the open or short to voltage in the horn relay control circuit. The horn relay control circuit includes horn slip ring and horn switch. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | --
16 | Repair the open circuit or high resistance at the horn relay switch battery positive voltage circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | --
17 | Repair open circuit or high resistance i horn control circuit if necessary. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | --
18 | Repair open circuit or high resistance in horn ground circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 21 | --
19 | Replace the DIM. 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 horn. Is the horn working normally? | System OK | Go to Step 1