GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2005 🢒 Unit Repair 🢒 DTC 🢒 DTC B2750

Circuit Description

The body control module (BCM) controls the horn relay by grounding the control circuit of the horn relay coil. When the horn relay coil is grounded, the horn relay contacts close, applying voltage to the horn via the horn supply voltage circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2750 Horn Relay Output

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom

DTC Symptom Descriptor

01

Short to Battery

Conditions for Running the DTC

The only requirements are valid operating voltage and ground.

Conditions for Setting the DTC

The following condition exists for more than 125 milliseconds:

B2750 01

The BCM detects a short to the battery in the horn relay control when output is active.

Action Taken When the DTC Sets

B2750 01

The BCM disables the horn relay control until the next ignition cycle.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Test Description

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

  1. During the horn relay operation, listen for an audible click. Command the ON and the OFF states. Repeat the commands as necessary.

    2.

  2. This step tests for voltage at the coil side of the horn relay. The horn fuse supplies power to the coil side of the horn relay.

    3.

  3. This step tests for a short to voltage in the horn relay signal circuit.

    4.

  4. This step verifies that the BCM is providing ground to the horn relay.

Step

Action

Yes

No

Schematic Reference: Horn Schematics

Connector End View Reference: Horn Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, command the horn relay ON and OFF.

Does the horn relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the horn relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the battery positive circuit of the horn with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 12

4

  1. Turn ON the ignition, with the engine OFF.
  2. Probe the horn relay control circuit of the horn relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 8

Go to Step 5

5

  1. Connect a test lamp between the control circuit of the horn relay and the battery positive voltage circuit of the horn relay.
  2. With a scan tool, command the horn relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 10

Go to Step 6

6

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 9

7

Test the control circuit of the horn relay for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 11

8
  1. Turn ON the ignition, with the engine OFF.
  2. Test the control circuit of the horn relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 11

9

Test the horn relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 11

10

Inspect for poor connections at the horn relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 11

11

Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 11

12

Repair the open in the horn relay battery positive voltage circuit. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 15

--

13

Replace the horn relay.

Did you complete the replacement?

Go to Step 15

--

14

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK