1. Compressor/Air Tank Issues:
- Check if the air compressor or tank is supplying enough air pressure.
- Look for leaks or damages in air lines or tank.
2. Wiring Problems:
- Inspect wiring connections; follow the air horn relay or air horn switch circuits for faulty wiring or loose connections.
- Check voltage to the air horn switch.
3. Horn Switch Faulty:
- Test the air horn switch to see if it sends a signal to the relay.
- Check for continuity or replace.
4. Defective Relay:
- Locate air horn relay and test it. Use a test light or multimeter to check power flow.
- Replace the relay if it's faulty.
5. Faulty Horn Assembly:
- Check horn assembly for any blockages or damage.
- Test horn continuity; replace if faulty.
6. System Malfunction:
- Check if there are any fault codes or messages on the vehicle's diagnostic system related to horn malfunction.
Steps to Diagnose and Fix:
1. Check Air Pressure:
- Locate air tank near the compressor.
- Check pressure gauge, typically labeled "Air Supply" if present, to ensure there is sufficient pressure for air horns to operate.
- If pressure is too low, it's possible the air compressor isn't functioning correctly. This could also affect brakes and air suspension systems on the vehicle.
2. Check Wiring:
- Follow the wiring from air horn switch to air horn relay and then to horn assembly.
- Look for loose connections or damaged wiring.
- Check for power (usually 12V) at the air horn switch and the input side of the air horn relay.
- Check that the output side of air horn relay has voltage when switch is pressed (this powers horn assembly).
3. Test Horn Switch:
- Locate air horn switch.
- Using a multimeter, check for continuity across switch contacts when air horn button is pressed. If no continuity, switch is faulty.
4. Test Horn Assembly:
- Remove horn assembly and test for continuity between its power terminal and ground.
- If there is no continuity, replace horn assembly.
5. Check Relay:
- Use a relay tester or multimeter to check its functionality.
- Replace the relay if it doesn't work.
6. Check for DTCs:
- Connect an OBD-II scanner to vehicle's diagnostic port and check for any air horn-related fault codes.
- Address any reported DTCs accordingly.
Note: Troubleshooting procedures may vary depending on specific Fuso Super Great model. Refer to vehicle-specific service manual for exact diagnostic steps.
