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Horn System: Diagnosis Chevrolet Sonic I

Horns ~1907 words

Diagnostic Code Index

DTCDescription
DTC B2750DTC B2750 Horn Relay Secondary Circuit

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(ref-542476-S03610919532013041600000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-542476-S11988299792013041600000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-542476-S27446858652013041600000) provides an overview of each diagnostic category.

DTC Descriptors

For symptom byte information refer to: Symptom Byte List

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
ControlB2750 02B2750 04B2750 01

Conditions for Running the DTC

When the horn output is actively being requested by the Body Control Module.

Conditions for Setting the DTC

B2750 01

The Body Control Module detects a short to voltage in the horn relay control circuit.

B2750 02

The Body Control Module detects a short to ground in the horn relay control circuit.

B2750 04

The Body Control Module detects an open/high resistance in the horn relay control circuit.

Action Taken When the DTC Sets

B2750 01, B2750 04

The Body Control Module will command the horn when requested but the horn will be inoperative.

B2750 02

The horn will sound continuously until the horn is disconnected or when the horn overheats and becomes inoperative.

Conditions for Clearing the DTC

  1. The DTC clears when the fault is no longer detected.
  2. The current DTC will become history when the request for the output is removed.
  3. The history DTC will clear after 50 consecutive fault-free ignition cycles have occurred.

Circuit/System Testing

  1. Ignition OFF, disconnect the X1 harness connector at the X50A Fuse Block-Underhood, ignition ON.
  2. Verify the P12 Horn is not activated. If the P12 Horn is activated Ignition OFF, disconnect the harness connector at the P12 Horn, ignition ON. Test for less than 1 V between the control circuit terminal 2 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, test or replace the P12 Horn. If the P12 Horn is not activated
  3. Connect a 15A fused jumper wire between the control circuit terminal D4 and B+.
  4. Verify the P12 Horn activates. If the P12 Horn does not activate Ignition OFF, remove the jumper wire, disconnect the harness connector at the P12 Horn, ignition ON. Test for infinite resistance between the control circuit and ground. If less than Infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test or replace the P12 Horn. If the P12 Horn activates
  5. Ignition OFF, connect the X1 harness connector at the X50A Fuse Block-Underhood. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  6. Verify the P12 Horn is not activated. If the P12 Horn is activated Ignition OFF, disconnect the X2 harness connector at the X50A Fuse Block-Underhood. Test for infinite resistance between the control circuit terminal 19 X5 at the K9 Body Control Module and ground. If less than Infinite resistance, repair the short to ground on the circuit. If infinite resistance, test or replace the X50A Fuse Block-Underhood. If the P12 Horn is not activated
  7. Connect a 3 A fused jumper wire between the control circuit terminal 19 and ground.
  8. Verify the P12 Horn activates. If the P12 Horn does not activate Ignition OFF, remove the jumper wire, disconnect the X2 harness connector at the X50A Fuse Block-Underhood, ignition ON. Test for less than 1 V between the control circuit terminal 19 X5 at the K9 Body Control Module and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test or replace the X50A Fuse Block-Underhood. If the P12 Horn activates
  9. Replace the K9 Body Control Module.

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the horn system. Refer to «Checking Aftermarket Accessories»(ref-542498-S16706522532013041600000) .
  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).

Symptom List

Refer to a symptom diagnostic procedure Horns Malfunction in order to diagnose the symptom.

  1. Perform the «Diagnostic System Check - Vehicle»(ref-542476-S03610919532013041600000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-542476-S11988299792013041600000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-542476-S27446858652013041600000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Horn Switch Signal122
Horn Relay ControlB2750 02B2750 04B2750 01
Horn Control221
Horn Ground2
1. Horn Always On 2. Horn Inoperative

Diagnostic Aids

A short to ground in the horn relay control circuit or a short to voltage in the horn control circuit will cause the horns to sound continuously until the horns overheat and become inoperative.

Rotate the steering wheel while pressing the horn pad to identify intermittent and poor connections within the steering column.

If diagnosing a Horn- Poor Tone condition, inspect the following

  1. Debris or water in the horn assembly
  2. Proper horn mounting hardware torque-Refer to «Fastener Tightening Specifications»(ref-542514-S11334629572013041600000) .
  3. Debris in the joint where the horns attach to the vehicle
  4. Debris in direct contact with the horn
  5. Vehicle components vibrating while the horn is sounding

Horn Switch Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the X85 Steering Wheel Air Bag Coil. Ignition ON
  2. Verify the scan tool Horn Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the harness connector at the K9 Body Control Module. Test for infinite resistance between the signal circuit terminal 1 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 Body Control Module. If Inactive
  3. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground.
  4. Verify the scan tool Horn Switch parameter is Active. If not Active Ignition OFF, remove the jumper wire, disconnect the harness connector at the K9 Body Control Module, ignition ON. Test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 Body Control Module. If Active
  5. Test or replace the S33 Horn Switch.

Horns or Horn Command Malfunction

  1. Ignition OFF, and all vehicle systems OFF. Disconnect the harness connector at the P12 Horn. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 1 ohms between the ground circuit terminal 1 and ground. If 1 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 1 ohms
  3. Connect a test lamp between the control circuit terminal 2 and ground, ignition ON.
  4. Verify the test lamp does not turn ON and OFF when commanding the Horn Relay On and Off with a scan tool. If the test lamp turns ON and OFF Test or replace the P12 Horn. If the test lamp does not turn ON and OFF
  5. Ignition OFF, connect the harness connector at the P12 Horn. Disconnect the X1 harness connector at the X50A Fuse Block-Underhood, ignition ON.
  6. Verify the P12 Horn is not activated. If the P12 Horn is activated Ignition OFF, disconnect the harness connector at the P12 Horn, ignition ON. Test for less than 1 V between the control circuit terminal 2 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, test or replace the P12 Horn. If the P12 Horn is not activated
  7. Connect a 15 A fused jumper wire between the control circuit terminal D4 and B+.
  8. Verify the P12 Horn activates. If the P12 Horn does not activate Ignition OFF, remove the jumper wire, disconnect the harness connector at the P12 Horn, ignition ON. Test for infinite resistance between the control circuit and ground. If less than Infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test or replace the P12 Horn. If the P12 Horn activates
  9. Ignition OFF, connect the X1 harness connector at the X50A Fuse Block-Underhood. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  10. Verify the P12 Horn is not activated. If the P12 Horn is activated Ignition OFF, disconnect the X2 harness connector at the X50A Fuse Block-Underhood. Test for infinite resistance between the control circuit terminal 19 X5 at the K9 Body Control Module and ground. If less than Infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the X50A Fuse Block-Underhood. If the P12 Horn is not activated
  11. Connect a 3 A fused jumper wire between the control circuit terminal 19 and ground.
  12. Verify the P12 Horn activates. If the P12 Horn does not activate Ignition OFF, remove the jumper wire, disconnect the X2 harness connector at the X50A Fuse Block-Underhood, ignition ON. Test for less than 1 V between the control circuit terminal 19 X5 at the K9 Body Control Module and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the X50A Fuse Block-Underhood. If the P12 Horn activates
  13. Replace the K9 Body Control Module.

Horn - Poor Tone

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the P12 Horn. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 1 ohms between the ground circuit terminal 1 and ground. If 1 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the high resistance in the circuit. If less than 2 ohms, repair high resistance in the ground connection. If less than 1 ohms
  3. Ignition OFF, disconnect the X1 harness connector at the X50A Fuse Block-Underhood.
  4. Test for less than 2 ohms between the P12 Horn control circuit terminal 2 and the X50A Fuse Block-Underhood control circuit terminal D4 X1. If 2 ohms or greater Repair the high resistance in the control circuit. If less than 2 ohms
  5. Test or replace the P12 Horn.

Component Testing

Horn Test

  1. Ignition OFF, disconnect the harness connector at the P12 Horn.
  2. Install a 15 A fused jumper wire between the control terminal 2 and 12 V. Install a jumper wire between the ground terminal 1 and ground.
  3. Verify the P12 Horn turns ON and OFF If the P12 Horn does not turn ON and OFF Replace the P12 Horn. If the P12 Horn turns ON and OFF
  4. All OK

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