GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Terraza Ext. 🢒 Brakes 🢒 Park Brake 🢒 DTC B2750

DTC Descriptor

DTC B2750 01: Relay Coil Control Circuit Short to Battery

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Horn Relay B+

2

2

--

--

Horn Relay Control

1

2

B2750

--

Horn Assembly Control

2

2

1

--

Horn Switch Ground

--

2

2

--

Horn Assembly Ground

--

2

2

--

1. Horn Always On

2. Horn 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

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.

Reference Information

Schematic Reference

Horn Schematics

Connector End View Reference

Horn Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

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 HORN relay.
  2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal and ground
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  3. Connect a test lamp between the relay coil control circuit terminal and the relay coil B+ circuit terminal.
  4. Command the horns ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    5. ⇒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.
    ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM
  5. If all circuits test normal, test or replace the HORN relay.

Component Testing
  1. Ignition OFF, disconnect the HORN relay.
  2. Test for 60-180 ohms between terminals 85 and 86.
    3. ⇒If not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒ If not the specified value, replace the relay.
  4. Install a 30-amp 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 between terminals 30 and 87.
    5. ⇒If greater than the specified range, replace the relay.

Repair Instructions
    •  Relay Replacement
    •  Control Module References for BCM replacement, setup and programming