GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 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.

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 Diagnostic Trouble Code (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 MIL/DTC

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

Test Description

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

  1. Listen for an audible click when the horn relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. 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. Verifies that the BCM is providing ground to the horn relay.

    4.

  4. Tests if ground is constantly being applied 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 Body Control System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

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

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

Go to Diagnostic Aids

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 voltage circuit of the horn relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  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 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the control circuit of the horn relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

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

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

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

Did you complete the repair?

Go to Step 13

--

11

Replace the horn relay.

Did you complete the replacement?

Go to Step 13

--

12

Important: Perform the set up procedure for the BCM.

Replace the BCM. Refer to Body Control Module Replacement in Computer/Integrating Systems.

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK