Pinpoint Test A: The Horn Is Inoperative - Except Stripped Chassis
Horn
Pinpoint Test A: The Horn Is Inoperative - Except Stripped Chassis
Normal Operation
The Smart Junction Box (SJB) supplies the control and switched voltage to the horn relay (integrated into the SJB (Smart Junction Box)). When the driver air bag is pressed, the horn switch (part of the driver air bag module) supplies ground through the clockspring to the horn relay coil (integrated into the SJB (Smart Junction Box)). The horn relay is then energized, routing voltage to the horn, enabling the horn to sound.
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 (Smart Junction Box)
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.
A1 CHECK THE SJB (Smart Junction Box) OUTPUT
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: SJB (Smart Junction Box) DataLogger.
- Select the SJB (Smart Junction Box) 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.
A2 CHECK FOR VOLTAGE TO THE CLOCKSPRING
- Depower the Supplemental Restraint System (SRS). Refer to Restraints and Safety Systems &/or Air Bag Systems.
- Disconnect: Clockspring C218B.
- Connect: Negative Battery Cable.
- Measure the voltage between the clockspring C218B-5, circuit CRH02 (BU/WH), harness side and ground.
Is the voltage greater than 10 volts?
Yes
GO to A4.
No
GO to A3.
A3 CHECK THE HORN RELAY COIL GROUND CIRCUIT FOR AN OPEN
- Disconnect: SJB (Smart Junction Box) C2280B.
- Measure the resistance between the SJB (Smart Junction Box) C2280B-41, circuit CRH02 (BU/WH), harness side and the clockspring C218B-5, 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 (Supplemental Restraint System). REFER to Restraints and Safety Systems &/or Air Bag Systems. TEST the system for normal operation.
A4 CHECK FOR VOLTAGE TO THE CLOCKSPRING USING THE CONNECTOR GROUND
- Measure the voltage between the clockspring C218B-5, circuit CRH02 (BU/WH), harness side and the clockspring C218B-7, 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 (Supplemental Restraint System). REFER to Restraints and Safety Systems &/or Air Bag Systems. TEST the system for normal operation.
A5 CHECK THE CLOCKSPRING FOR AN OPEN
- Inspect the clockspring for an open.
Is the clockspring OK?
Yes
GO to A6.
No
INSTALL a new clockspring. TEST the system for normal operation.
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.
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 (Smart Junction Box) 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 Electrical Diagrams.
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 Horn. TEST the system for normal operation.
No
REPAIR circuit GD129 (BK/YE) for an open. TEST the system for normal operation.
A9 CHECK THE HORN VOLTAGE SUPPLY CIRCUIT FOR AN OPEN
- Disconnect: SJB (Smart Junction Box) C2280E.
- Measure the resistance between the SJB (Smart Junction Box) 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.
A10 CHECK FOR CORRECT SJB (Smart Junction Box) OPERATION
- Disconnect all the SJB (Smart Junction Box) connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB (Smart Junction Box) 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 (Smart Junction Box). 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.