B2750

DTC B2750

Diagnostic Instructions

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

DTC Descriptor
DTC B2750 01
- Horn Relay Control Circuit Short to Battery

Diagnostic Fault Information






Circuit/System Description

Battery positive voltage is applied at all times to the horn relay coil and horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module (BCM) also may apply ground to the horn relay control circuit. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn via the horn control circuit. The horn will sound as long as ground is applied to the horn relay control circuit.

Conditions for Running the DTC

The BCM monitors the voltage level on the horn relay control circuit whenever the ignition is in the RUN position.

Conditions for Setting the DTC

The BCM will set DTC B2750 as current whenever an improper voltage level is detected on the horn relay control circuit for more than 15 seconds.

Action Taken When the DTC Sets

The BCM will disable the driver for the horn relay control circuit whenever DTC B2750 is set as current.

Conditions for Clearing the DTC

DTC B2750 will clear when an improper voltage level is no longer detected on the horn relay control circuit, or when a scan tool is used to clear DTCs.

Diagnostic Aids

Inspect for a sticking horn pad or horn switch.

Circuit/System Verification

1. Press the horn switch. The horn relay should click and the horn should sound as long as the horn switch is pressed.
2. Turn ON the ignition. With a scan tool, command the BCM Horn Output. The horn relay should click and the horn should sound while commanded ON and stop sounding when commanded OFF.

Circuit/System Testing

1. Ignition OFF, disconnect the horn relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal 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 tests normal and the B+ circuit fuse is open, test the control circuit terminal for a short to ground. If the circuit tests normal, test or replace the horn relay.

4. Connect a test lamp between the B+ circuit terminal and the relay control circuit terminal.
5. Command the horn output ON and OFF using a scan tool. The test lamp should turn ON and OFF when changing between the command states.

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

• 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.

6. If all circuits test normal, test or replace the Horn Relay.

Component Testing

Relay Test
1. Ignition OFF, disconnect the HORN relay.
2. Test for less than 200 ohms resistance between terminals 85 and 86.

• If resistance is not in 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. Test for less than 2 ohms of resistance between terminals 30 and 87A.

• If greater than the specified range, replace the relay.

5. Install a 10A 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 of resistance between terminals 30 and 87.

• If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification prior to using this diagnostic procedure. Verification Tests

* Inflatable Restraint Steering Wheel Module Coil Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Control Module References for BCM replacement, setup, and programming Programming and Relearning