B2750

DTC B2750 (RPO LS4) (5.3L)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.

DTC Descriptor
DTC B2750
- Horn Relay Coil Circuit

Diagnostic Fault Information





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 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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Horns System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)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 X2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal K3 and B+.
3. Press and release the horn switch. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to ground or a sticking horn switch. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage, an open high resistance, or a horn switch which is not closing. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, replace the underhood fuse block.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Control Module References (Programming and Relearning)for BCM replacement, setup, and programming