Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is diagnosing an intermittent issue with a vehicle's horn that occasionally does not work. The horn is controlled by a relay, which in turn is activated by a steering wheel switch through a control module. When the horn does not work, the technician uses a digital multimeter and confirms there is battery voltage at the horn relay's power input (terminal 30) and at its control side power input (terminal 86). However, there is no ground at the control side ground terminal (terminal 85) when the horn button is pressed. What should the technician check NEXT?
- AThe resistance of the horn itself
- BThe continuity of the wire from the relay's load side output to the horn
- CThe current draw of the horn circuit
- DThe voltage at the horn switch input to the control module
Show answer & explanationAnswer & explanation
Correct answer: D. The voltage at the horn switch input to the control module
The absence of ground at terminal 85 when the horn button is pressed indicates the control circuit is not completing the ground path for the relay coil. Since the horn button activates a control module, the next logical step is to verify if the module is receiving the input signal from the horn button.
Why the other options are wrong
- A. The horn itself is not receiving power due to the relay not activating, so checking its resistance is premature.
- B. This would be the next step if the relay was activating but no power reached the horn. Here, the relay isn't activating.
- C. Current draw is only relevant if the circuit is working; here, the circuit isn't completing.
Relay Control Input
The electrical signal (power or ground) that activates the relay coil, causing the relay's internal contacts to switch and complete a higher-current circuit.
- Activates the relay coil
- Can be positive (power) or negative (ground) triggered
- Absence prevents relay operation
Memory trick: No ground to the relay, check the button's way.