For 1990-2009 cars

### Diagnostic Instructions

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

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B2750 00: Horn Relay Coil Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Horn Relay B+ | 2 | 2 | -- | --
Horn Relay Control | B2750 00 | B2750 00 | B2750 00 | --
Horn Control | 2 | 2 | 1 | --
Horn Switch Ground | -- | 2 | 2 | --
Horn Ground | -- | 2 | 2 | --
1. Horn Always On 2. Horn Inoperative

### Circuit/System Description

The body control module (BCM) controls the horn relay by grounding the control circuit of the horn relay coil energizing the relay. When the horn relay is energized, the horn relay contacts close applying voltage through the horn fuse and the horn control circuit to the horns.

### Conditions for Running the DTC

When the horn output is actively being requested by the BCM.

### Conditions for Setting the DTC

The BCM detects a short to ground, open, or short to voltage in the horn relay control circuit for approximately 125 milliseconds.

### Action Taken When the DTC Sets

The BCM disables the output to the horn relay until the next ignition cycle.

### Conditions for Clearing the DTC

• | The DTC clears when the fault is no longer detected.

• | The current DTC will become history when the request for the output is removed.

• | The history DTC will clear after 50 consecutive fault-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Horn Schematics

#### Connector End View Reference

Component 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

Control Module References for scan tool information

### Circuit/System Verification

Command the horns ON and OFF with the scan tool. The horns should turn ON and OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the HORN relay.
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 85 and ground

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuit terminal 87 for a short to ground. If all circuits test normal, test or replace the HORN relay.

3. Connect a test lamp between the control circuit terminal 86 and the B+ circuit terminal 85.
4. Command the horns ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | 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 BCM.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM

5. If all circuits test normal, test or replace the HORN relay.

### Component Testing

1. Ignition OFF, disconnect the horn relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

⇒ | If greater than the specified range, replace the relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for BCM replacement, setup and programming