Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is diagnosing an intermittent issue where a vehicle's horn occasionally does not work. The horn relay clicks when activated, but no sound is produced. A quick check shows the horn fuse is good. What is the MOST appropriate next diagnostic step?
- AInspect the horn button circuit.
- BPerform a continuity test on the horn's ground wire.
- CCheck for voltage at the horn's power terminal.
- DReplace the horn relay.
Show answer & explanationAnswer & explanation
Correct answer: C. Check for voltage at the horn's power terminal.
The horn relay clicking indicates that the control circuit (including the horn button and relay coil) is functioning. Since the fuse is good, the next logical step is to verify if the relay is actually passing power to the horn itself. Checking for voltage at the horn's power terminal will determine if the relay's load contacts are closing and delivering power.
Why the other options are wrong
- A. The horn button circuit is working, as indicated by the relay clicking.
- B. While a ground issue could be present, verifying power to the horn is the immediate next step to isolate the problem to either power delivery or the horn itself/its ground.
- D. The relay clicks, so replacing it without further testing is premature. The click indicates the coil is working; the load contacts might be bad, but testing for voltage confirms this.
Relay Load Side Output Diagnosis
A diagnostic process focused on verifying the power delivery through the load contacts of a relay, especially when the relay coil is known to be activating.
- If a relay clicks, its control circuit and coil are likely good.
- The fault then lies in the load side of the relay, the wiring to the load, or the load itself.
- Checking for voltage at the load's input terminal directly tests the relay's output and power path.
Memory trick: Click means control's good, but power's stuck, check the horn's juice, don't get stuck.