Pinpoint Test A: The Horn Is Inoperative
Horn
Pinpoint Tests
Pinpoint Test A: The Horn Is Inoperative
Refer to Wiring Diagram Set 44 (Fusion/Milan/MKZ, Fusion Hybrid/Milan Hybrid), Horn/Cigar Lighter for schematic and connector information. Diagrams By Number
Normal Operation
The Smart Junction Box (SJB) supplies the switched and control voltage to the horn relay (part of the SJB). When the horn switches (part of the steering wheel) are pressed, the switches are grounded to the steering wheel. Ground is then supplied to the horn relay, energizing the horn relay. The horn relay then sends voltage to the horn, enabling the horn to sound. The horn assembly has its own ground.
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- Horn
- Clockspring
- Steering wheel harness
- Horn switches (part of the steering wheel)
- SJB
PINPOINT TEST A: THE HORN IS INOPERATIVE
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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A1 CHECK THE SJB OUTPUT
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: SJB DataLogger.
- Select the SJB horn PID (HORN). Active command the horn on and then off.
- Does the horn sound when commanded on?
Yes
GO to A2.
No
VERIFY the SJB fuse 24 (20A) is OK. If OK, GO to A6. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short Diagrams By Number.
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A2 CHECK FOR VOLTAGE TO THE CLOCKSPRING
- Connect: Negative Battery Cable.
- Measure the voltage between the clockspring C218a-8, circuit CRH02 (BU/WH), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to A4.
No
GO to A3.
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A3 CHECK THE HORN RELAY COIL GROUND CONTROL CIRCUIT FOR AN OPEN
- Disconnect: SJB C2280b.
- Measure the resistance between the SJB C2280b-41, circuit CRH02 (BU/WH), harness side and the clockspring C218a-8, circuit CRH02 (BU/WH), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to A9.
No
REPAIR circuit CRH02 (BU/WH) for an open. REPOWER the SRS. REFER to Restraint Systems. TEST the system for normal operation.
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A4 CHECK THE STEERING WHEEL HARNESS FOR AN OPEN
- Disconnect: Horn Switch C2996 and C2997.
- Measure the resistance between the upper clockspring C218b-1, circuit CRH02 (BU/WH), harness side and the horn switch C2996-1, circuit CRH02 (BU/WH), harness side; and between the upper clockspring C218b-1, circuit CRH02 (BU/WH), harness side and the horn switch C2997-1, circuit CRH02 (BU/WH), harness side.
- Are the resistances less than 5 ohms?
Yes
GO to A5.
No
REPAIR circuit CRH02 (BU/WH) for an open. INSTALL the driver air bag module. REFER to Restraint Systems. TEST the system for normal operation.
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A5 CHECK THE CLOCKSPRING FOR AN OPEN
- Measure the resistance between the clockspring C218a pin 8, component side and the clockspring C218b pin 1, component side.
- Is the resistance less than 5 ohms?
Yes
INSTALL a new steering wheel. REFER to Steering Column. TEST the system for normal operation.
No
INSTALL a new clockspring. REFER to Restraint Systems. TEST the system for normal operation.
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A6 CHECK FOR VOLTAGE TO THE HORN
- Disconnect: Horn C131.
- While pressing the horn switch, measure the voltage between the horn C131-2, circuit SRH01 (YE/RD), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to A7.
No
GO to A8.
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A7 CHECK FOR VOLTAGE TO THE HORN USING THE CONNECTOR GROUND
- While pressing the horn switch, measure the voltage between the horn C131-2, circuit SRH01 (YE/RD), harness side and the horn C131-1, circuit GD123 (BK/GY), harness side.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new horn. REFER to Horn Service and Repair. TEST the system for normal operation.
No
REPAIR circuit GD123 (BK/GY) for an open. TEST the system for normal operation.
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A8 CHECK THE HORN VOLTAGE SUPPLY CIRCUIT FOR AN OPEN
- Disconnect: SJB C2280e.
- Measure the resistance between the SJB C2280e-5, circuit SRH01 (YE/RD), harness side and the horn C131-2, circuit SRH01 (YE/RD), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to A9.
No
REPAIR circuit SRH01 (YE/RD) for an open. TEST the system for normal operation.
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A9 CHECK FOR CORRECT SJB OPERATION
- Disconnect all the SJB connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new SJB. REFER to Body Control Systems. REPOWER the SRS. REFER to Restraint Systems. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. REPOWER the SRS. REFER to Restraint Systems.
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