Horn System Cadillac XLR I

Fastener Tightening Specifications

Fastener Tightening Specifications

Scheme 1

Scheme 2

Scheme 3

Horn Connector End Views

Horn Assembly

Diagnostic Starting Point - Horns

Begin the system diagnosis with the Diagnostic System Check - Vehicle in Vehicle DTC Information. The Diagnostic System Check - Vehicle will provide the following information

1. The identification of the control modules which command the system
2. The ability of the control modules 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 - Vehicle will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

Scan Tool Output Controls

Scan Tool Data List

The Horns Scan Tool Data List contains all of the 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 - Vehicle in Vehicle DTC Information.

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.

Scan Tool Data List

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.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B2750 Horn Relay Coil 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 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. 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 BCM is providing ground to the horn relay.
4. 5: Tests if ground is constantly being applied to the horn relay.

DTC B2750

Symptoms - Horns

1. On vehicles equipped with content theft deterrent (UA6), perform «Diagnostic System Check - Vehicle»(/cadillac/xlr/i-2003-2009/remont/oem-general-information/#vehicle-dtc-information) before using the symptom tables in order to verify that there are no DTCs set.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Horns System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/horns/#horn-system) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the horn system. Refer to «Checking Aftermarket Accessories»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Perform the following if a horn buzzes or has a harsh tone: Inspect for debris in the joint where the horn fastens 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).

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Horns Always On»(/cadillac/xlr/i-2003-2009/remont/horns/#horn-system)
2. «Horns Inoperative»(/cadillac/xlr/i-2003-2009/remont/horns/#horn-system)
3. «Horns - Poor Tone»(/cadillac/xlr/i-2003-2009/remont/horns/#horn-system__horns-poor-tone)

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 slip ring and the horn switch. The horn slip ring and horn switch must be tested for a short to ground when testing the relay control circuit. Refer to «Circuit Testing»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__circuit-testing) and «Wiring Repairs»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__wiring-repairs) in Wiring Systems.

Horns Always On

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 battery power 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 0.5 ohms, 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 slip ring and the horn switch. The horn slip ring and horn switch must be tested for a high resistance, an open or a short to voltage when testing the relay control circuit. Refer to «Circuit Testing»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__circuit-testing) and «Wiring Repairs»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__wiring-repairs) in Wiring Systems.

Horns Inoperative

Horns - Poor Tone

Horns - Poor Tone

Removal Procedure

1. Remove the right front fascia lower closeout panel. Refer to «Front Bumper Fascia Lower Close Out Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/exterior-body-panels/#bumper-system) .
2. Disconnect the horn assembly electrical connector.
3. Remove the horn assembly bolt.
4. Remove the horn assembly from the skid bar.

Installation Procedure

1. Position the horn assembly to the skid bar. Install the aligning tab on the horn assembly into the hole on the skid bar.
2. Install the horn assembly bolt. Tighten: Tighten the bolt to 25 N.m (18 lb ft).
3. Connect the horn assembly electrical connector.
4. Install the right front fascia lower closeout panel. Refer to «Front Bumper Fascia Lower Close Out Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/exterior-body-panels/#bumper-system) .

System Description

The horn system consists of the following components

1. Horn relay
2. Inflatable restraint steering wheel module coil
3. Horn switch
4. Horn assembly
5. Body control module (BCM)

System Operation

The vehicle horn system is 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 any 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»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#theft-deterrent-system__content-theft-deterrent-ctd-description-and) . When the panic button is depressed on the remote control door lock transmitter-For further information refer to «Keyless Entry System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#keyless-entry-system) . When the keyless entry system is used, a horn chirp may sound to notify the driver that a keyless entry event has occurred. The notification feature may be enabled or disabled through personalization-For further information refer to «Keyless Entry System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#keyless-entry-system) .

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 horns through the horn control circuit. The horns sound as long as ground is applied to the horn relay control circuit.

See also:
• Diagnostic System Check - Vehicle
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Control Module References
• Checking Aftermarket Accessories
• Front Bumper Fascia Lower Close Out Panel Replacement
• FASTENER NOTICE
• Content Theft Deterrent (CTD) Description and Operation
• Keyless Entry System Description and Operation
• Horn Schematics
• Horns - Poor Tone
• Symptoms - Horns
• Fastener Tightening Specifications