Horn System Cadillac Escalade GMT800

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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.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. 2. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 4. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

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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.

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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.

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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 AND POOR CONNECTIONS in Wiring Systems.

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

1. 2. Listen for an audible click when the horn relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3. 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. 4. Verifies that the body control module (BCM) is providing ground to the horn relay.
4. 5. Tests if ground is constantly being applied to the horn relay.

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Symptoms-Horns

Important: The following steps must be completed before using the symptom tables.

1. Perform «DIAGNOSTIC SYSTEM CHECK-HORNS»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system) before using the symptom tables in order to verify that all of the following are true: There are no DTCs set. The body control module (BCM) can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «HORNS SYSTEM DESCRIPTION AND OPERATION»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system) .

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 in Wiring Systems.
2. Inspect the easily accessible or visible system components and harness connectors for obvious damage or conditions which could cause the symptom. NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
3. 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).

Intermittents

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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. «HORNS ALWAYS ON»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system)
2. «HORNS INOPERATIVE»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system)
3. «HORNS INOPERATIVE-ONE HORN»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system)
4. «HORNS-POOR TONE»(/cadillac/escalade/gmt800-2001-2006/remont/horns/#horn-system)

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

1. 4. Tests if ground is constantly being applied to the horn relay.
2. 5. The horn relay control circuit includes the horn switch. The horn switch must be tested for a short to ground when testing the relay control circuit.

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

1. 4. Verifies that the body control module (BCM) is providing ground to the horn relay.
2. 5. Tests for voltage at the battery positive voltage terminal of the horn relay coil.
3. 7. Tests for voltage at the battery positive voltage terminal of the horn relay switch. The HORN fuse supplies power to the battery positive voltage terminal of the horn relay switch.
4. 13. The horns need maximum current flow to operate properly. A high resistance (greater than 0.5ohms) in the horn control circuit or the horn ground circuit could cause operating problems with the horns. Inspect the circuits for faults that would restrict current flow.
5. 15. The horn relay control circuit includes the horn switch. The horn switch must be tested for a high resistance, an open or a short to voltage when testing the relay control circuit.

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The number below refers to the step number on the diagnostic table.

1. 9. The horns need maximum current flow to operate properly. A high resistance - greater than 0.5ohms - in the horn control circuit or the horn ground circuit could cause operating problems with the horns. Inspect the circuits for faults that would restrict current flow.

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Removal Procedure

1. Raise the hood.
2. Remove the battery. Refer to BATTERY REPLACEMENT in Engine Electrical.
3. Remove the battery tray. Refer to BATTERY TRAY REPLACEMENT in Engine Electrical.
4. Remove the washer reservoir. Refer to WASHER PUMP/RESERVOIR REPLACEMENT in Wipers/Washer Systems.
5. Raise and suitably support the vehicle.
6. Disconnect the horn electrical connector.
7. Remove the horn bolt. Reposition the park/turn signal lamp wiring harness for additional clearance.
8. Remove the horn (2) from the radiator support (1).

Installation Procedure

Important: Ensure that the black side of the horn is facing forward on the vehicle.

1. Install the horn (2) to the radiator support (1). NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
2. Install the horn bolt. Tighten Tighten the horn bolts to 9 N.m (80 lb in).
3. Connect the horn electrical connector.
4. Lower the vehicle.
5. Install the washer reservoir. Refer to WASHER PUMP/RESERVOIR REPLACEMENT in Wipers/Washer Systems.
6. Install the battery tray. Refer to BATTERY TRAY REPLACEMENT in Engine Electrical.
7. Install the battery. Refer to BATTERY REPLACEMENT in Engine Electrical.
8. Close the hood.

1. Raise and suitably support the vehicle.
2. Disconnect the horn electrical connector.
3. Remove the horn bolt. Reposition the park/turn signal lamp wiring harness for additional clearance.
4. Remove the horn (2) from the radiator support (1).

Important: Ensure that the black side of the horn is facing forward on the vehicle.

1. Install the horn (2) to the radiator support (1). NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
2. Install the horn bolt. Tighten Tighten the horn bolts to 9 N.m (80 lb in).
3. Connect the horn electrical connector.
4. Lower the vehicle.

System Description

The horn system consists of the following components

1. Horn fuse
2. Horn relay
3. Horn switch
4. Horn(s)
5. Body Control Module (BCM)

System Operation

The vehicle horns are activated under the following conditions

1. The horn switch is depressed.
2. The body control module (BCM) commands the horns on. The BCM commands the horns on under either of the following conditions: When the content theft deterrent system detects a vehicle intrusion. For further information, Refer to CONTENT THEFT DETERRENT (CTD) DESCRIPTION AND OPERATION in Theft Deterrent. When the panic button is depressed on the remote control door lock transmitter. For further information, Refer to KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION in Keyless Entry. When the OnStar® system is used to sound the horns, if equipped. For further information, Refer to ONSTAR DESCRIPTION AND OPERATION in Cellular Communications. When the keyless entry system is used to lock the vehicle, a horn chirp may sound to notify the driver that the vehicle has been locked. The notification feature may be enabled or disabled through personalization. For further information, Refer to KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION in Keyless Entry.

Circuit Operation

Battery positive voltage is applied at all times to the horn relay coil and the horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module BCM may also apply ground to the horn relay control circuit as described above. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn(s) through the horn control circuit. The horn(s) sound as long as ground is applied to the horn relay control circuit.

See also:
• DIAGNOSTIC SYSTEM CHECK-HORNS