For 1990-2009 cars
Body Control Module Components
Body Control System Schematics

### Circuit Description

CKT 28 is an input to the body control module (BCM). The BCM monitors CKT 28 to determine if the horn circuit is shorted to ground. When CKT 28 is shorted to ground for 30 seconds the BCM sets DTC B2752.

### Conditions for Setting the DTC

• | When CKT 28 is shorted to ground and the BCM is not commanding the horn relay ON.

• | The system voltage must be between 9.0-16.0 volts.

• | The above conditions must be met for 30 seconds.

### Action Taken When the DTC Sets

The BCM stores DTC B2752 in memory.

### Conditions for Clearing the DTC

• | A current DTC clears after the next fault free ignition cycle.

• | A history DTC clears after 100 consecutive ignition cycles without a fault present.

• | Clear history and current DTCs using a Scan Tool scan tool.

### Diagnostic Aids

• | If the DTC is a history DTC, the problem may be intermittent. Try performing the above tests while wiggling the wiring and connectors. This can often cause the malfunction to appear.

• | Check for a sticking horn pad and/or switch.

• | Using a J 39200 Digital Multi-Meter , compare the scan tool values to the actual BCM values.

• | Perform a visual check of the wiring and connectors

• | For an open circuit, the horn will be inoperative

• | For a short to ground, the horn will sound continually until the fuse blows.

### Test Description

The numbers below refer to the numbers in the diagnostic table.

1. This step tests the horn relay for proper operation.

2. This step tests CKT 28 for a short to ground or an open within the underhood wiring harness junction block.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Important: A short to ground will cause an open fuse(s). Before performing this diagnostic procedure, inspect the fuse(s) for an open.
1 | Was the Body Control Module (BCM) System Check performed? | -- | Go to Step 2 | Go to the Body Control Module System Check
2 | Replace the horn relay with a known good relay on the underhood wiring harness junction block. Use the Scan Tool scan tool in order to enable the horn relay. Does the horn work properly? | -- | Go to Step 7 | Go to Step 3
3 |

1. Reconnect the horn relay on the underhood wiring harness junction block.
2. Disconnect the underhood wiring harness junction block connector C3 terminal C12, CKT 28.
3. Use the J 39200 Digital Multi-Meter in order to measure the voltage in CKT 28 between the underhood wiring harness junction block connector C3.

Is the measured voltage equal to the specified value?

B+

Go to Step 5

Go to Step 4

4 | Replace the underhood wiring harness junction block. Refer to Underhood Fuse Block Replacement in Engine Electrical. Is the circuit repair complete? | -- | Go to Step 7 | --
5 |

1. Disconnect the BCM connector C1.
2. Using J 39200 DMM, measure the resistance between BCM connector C1 terminal A4 and the underhood wiring harness junction block connector C3 terminal C12.

Is the measured resistance within the specified range?

0-2 ohms

Go to Step 7

Go to Step 6

6 | Repair the open in CKT 28 between BCM connector C1 and the underhood wiring harness junction block connector C3. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 7 | --
7 | Clear the DTC from memory. Is the DTC cleared from memory? | -- | Go to the Body Control Module System Check | --