A technician is diagnosing a vehicle with an intermittent no-start condition. The technician determines that the fuel pump is not operating. Using a wiring diagram, the technician identifies the fuel pump relay. When the ignition is turned to the 'ON' position, the technician hears the relay click, but the fuel pump does not run. What should the technician check NEXT?
- AThe fuel pump's ground circuit.
- BThe fuel pump relay's coil resistance.
- CThe voltage at the fuel pump relay's switched output.
- DThe fuel pump's internal resistance.
Show answer & explanationAnswer & explanation
Correct answer: C. The voltage at the fuel pump relay's switched output.
If the relay clicks, it means the control circuit (coil) is likely functioning and energizing the relay. However, a click does not guarantee that the relay's internal switched contacts are actually passing power to the fuel pump. The next logical step is to verify if voltage is present at the relay's switched output terminal to confirm power is being delivered from the relay to the fuel pump circuit.
Why the other options are wrong
- A. While a bad ground could prevent the pump from running, checking the relay's output voltage first confirms if power is even leaving the relay.
- B. The relay clicking indicates the coil is working, so measuring its resistance is not the immediate next step.
- D. Checking the fuel pump's internal resistance is relevant if power is reaching the pump, but first, confirm power is leaving the relay.
Relay Output Verification
After confirming a relay coil is energized (e.g., by hearing a click), the next diagnostic step is to verify that the relay's switched contacts are successfully passing power to its output circuit.
- A relay click means the coil is energized.
- Doesn't guarantee switched contacts are working.
- Measure voltage at output to confirm power delivery.
Memory trick: Click means 'I'm trying', but output shows if current's flying.