Pinpoint Test A: The Horn Is Inoperative - Except Stripped Chassis
Horn
Pinpoint Tests
Pinpoint Test A: The Horn Is Inoperative - Except Stripped Chassis
Refer to Wiring Diagram Set 44, Horn/Cigar Lighter for schematic and connector information. Diagrams By Number
Normal Operation
The Smart Junction Box (SJB) supplies the control and switched voltage to the horn relay (part of the SJB). When the driver air bag is pressed, the horn switch (part of the driver air bag module) supplies ground from circuit GD114 (BK/BU) through the clockspring to the horn relay coil (part of the SJB) through circuit CRH02 (BU/WH). The horn relay is then energized routing voltage to the horn through circuit SRH01 (YE/RD), enabling the horn to sound. Ground for the horn is supplied through circuit GD129 (BK/YE).
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- Horn
- Clockspring
- Steering wheel harness
- Horn switch (part of the driver air bag module)
- SJB
PINPOINT TEST A: THE HORN IS INOPERATIVE - EXCEPT STRIPPED CHASSIS
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). Command the horn on and then off.
- Does the horn sound when commanded on?
Yes
GO to A2.
No
GO to A7.
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A2 CHECK FOR VOLTAGE TO THE CLOCKSPRING
- Depower the Supplemental Restraint System (SRS). Refer to Air Bag Systems.
- Disconnect: Clockspring C218b.
- Connect: Negative Battery Cable.
- Measure the voltage between the clockspring C218b-3, 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 CIRCUIT FOR AN OPEN
- Disconnect: SJB C2280b.
- Measure the resistance between the SJB C2280b-41, circuit CRH02 (BU/WH), harness side, and the clockspring C218b-3, circuit CRH02 (BU/WH), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to A4.
No
REPAIR circuit CRH02 (BU/WH) for an open. REPOWER the SRS. REFER to Air Bag Systems. TEST the system for normal operation.
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A4 CHECK FOR VOLTAGE TO THE CLOCKSPRING USING THE CONNECTOR GROUND
- Measure the voltage between the clockspring C218b-3, circuit CRH02 (BU/WH), harness side and the clockspring C218b-4, circuit GD114 (BK/BU), harness side.
- Is the voltage greater than 10 volts?
Yes
GO to A5.
No
REPAIR circuit GD114 (BK/BU) for an open. REPOWER the SRS. REFER to Air Bag Systems. TEST the system for normal operation.
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A5 CHECK THE CLOCKSPRING FOR AN OPEN
- Remove the driver air bag module.
- Disconnect: Upper Clockspring Connector.
- Measure the resistance between the clockspring C218b pin 3, component side and the upper clockspring connector pin 3, component side.
- Measure the resistance between the clockspring C218b pin 4, component side and the upper clockspring connector pin 2, component side.
- Are the resistances less than 5 ohms?
Yes
GO to A6.
No
INSTALL a new clockspring. TEST the system for normal operation.
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A6 CHECK THE STEERING WHEEL HARNESS
- Inspect the steering wheel harness for damage or opens.
- Is the steering wheel harness OK?
Yes
INSTALL a new driver air bag module. TEST the system for normal operation.
No
REPAIR or INSTALL a new steering wheel harness. INSTALL the driver air bag module. TEST the system for normal operation.
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A7 CHECK FOR VOLTAGE TO THE HORN
- Ignition OFF.
- 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 A8.
No
VERIFY the SJB fuse 24 (20A) is OK. If OK, GO to A9. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short.
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A8 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 GD129 (BK/YE), 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 GD129 (BK/YE) for an open. TEST the system for normal operation.
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A9 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 A10.
No
REPAIR circuit SRH01 (YE/RD) for an open. TEST the system for normal operation.
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A10 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. 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. TEST the system for normal operation.
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