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 : Horn Relay Coil Circuit Shorted to Battery

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Horn Relay Control | 1 | 2 | B2750 00 | --
Horn Control | 2 | 2 | 2 | --
Horn Ground | -- | 2 | -- | --
Horn Switch Ground | -- | 2 | -- | --

1. Horns Always ON
2. Horns 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

The DTC can only set only when the output is actively being requested by the BCM.

### Conditions for Setting the DTC

The BCM detects a 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.

### Circuit/System Verification

Ignition ON, use scan tool horn output control to command the horn relay while listening for an audible click when commanding the horn relay ON and OFF.

### Circuit/System Testing

1. Ignition OFF, disconnect the J2 harness connector at the engine fuse block.
2. Connect a test lamp between the control circuit terminal 22 and battery voltage.
3. Command the horn 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 ON, test the horn relay control circuit for a short to ground. If the circuit tests normal, replace the body control module BCM.

⇒ | If the test lamp is always OFF, test the horn relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. If all circuits/connectors test normal, replace the engine fuse block.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

For BCM replacement, setup, and programming refer to Control Module References .