Horn Systems: Diagnosis Chevrolet Silverado 2500

Diagnostic Starting Point - Horns

Begin the system diagnosis with Diagnostic System Check - Horns . The Diagnostic System Check will provide the following information

1. The identification of the control module(s) which command the system.
2. The ability of the control module(s) to communicate through the serial data circuit
3. The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Data List

The Horns Scan Tool Data List contains all horn related parameters that are available on the scan tool. The parameters in the list are arranged in alphabetical order. The column, "Data List," indicates the location of the parameter within the scan tool menu selections. Use the Horns Scan Tool Data List as directed by a diagnostic table or in order to supplement the diagnostic procedures. Begin all of the diagnostic procedures with Diagnostic System Check - Horns .

Use the Scan Tool Data List only after the following is determined

1. There is no published DTC procedure nor published symptom procedure for the customer concern.
2. The DTC or symptom diagnostic procedure indicated by the diagnostic system check does not resolve the customer concern.

The Typical Data Values are obtained from a properly operating vehicle under the conditions specified in the first row of the Scan Tool Data List table. Comparison of the parameter values from the suspect vehicle with the Typical Data Values may reveal the source of the customer concern.

Scheme 9

Scan Tool Data Definitions

Battery Voltage: The scan tool displays the current state of the battery in volts.

Horn Relay: The scan tool displays the commanded state of the horn relay. The scan tool displays ON when the BCM applies ground to the horn relay to activate the horn(s).

Horn Relay Input: The scan tool displays the state of the horn relay. The scan tool displays ACTIVE when the BCM senses that the horn relay is being commanded ON by the relay coil circuit being grounded.

Scheme 10

Circuit Description

The vehicle horns are activated whenever ground is applied to the horn relay coil through the horn relay control circuit. Ground may be applied by either of the following

1. Body control module (BCM)
2. Horn switch

Conditions for Running the DTC

1. The body control system voltage must be between 9.0 and 16.0 volts.
2. The BCM is commanding the horn relay on or the horn switch is pressed.

Conditions for Setting the DTC

The BCM detects a short to ground or an open in the horn relay control circuit for approximately 3 minutes.

Action Taken When the DTC Sets

1. If the horn relay control circuit is shorted to ground the horns will remain ON at all times.
2. If the horn relay control circuit is open the horn will only work with the horn button on the steering wheel.
3. The BCM stores DTC B2752 in memory.

Conditions for Clearing the DTC

1. A current DTC will clear when the fault is no longer present and the ignition is cycled.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. A scan tool may be used to clear history and current DTC(s).

Diagnostic Aids

1. Always begin diagnosis with the first DTC listed on the scan tool.
2. The scan tool must display DTC B2752 as a current code before performing these diagnostics.
3. Inspect for a sticking horn pad and or switch.
4. Perform a visual inspection for loose or poor connections at all related components.

Refer to TESTING FOR INTERMITTENT & POOR CONNECTIONS .

Visual/Physical Inspection

Several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely important, it could lead to correcting a problem without further checks and can save valuable time. These checks include the following

1. Inspect for aftermarket devices which could affect the operation of the Horn System. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175672-S27030348872005042500000) .
2. Inspect the easily accessible or visible system components and harness connectors for obvious damage or conditions which could cause the symptom.

1. Perform the following if the horns buzz or have a harsh tone: Inspect for debris in the joints where the horns fasten to the vehicle. Test the torque of the horn mounting hardware. The horn mounting hardware should be tightened to a torque of 10 N.m (7 lb ft)

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose a symptom that does not set a DTC

1. See «Horns Always On»(ref-176701-S28860459062005051300000) .
2. See «Horns Inoperative»(ref-176701-S25036528392005051300000) .
3. See «Horns Inoperative - One Horn»(ref-176701-S13564938692005051300000) .
4. See «Horns - Poor Tone»(ref-176701-S42193691562005051300000) .