ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Medium
A client complains that their vehicle fails to start. The technician connects a spark tester to a spark plug wire and cranks the engine, observing no spark. Next, the technician uses a multimeter to check for voltage at the positive (+) terminal of the ignition coil. The multimeter reads battery voltage. What should the technician check next to diagnose the no-start condition?
- AThe resistance of the spark plug wires.
- BThe primary winding resistance of the ignition coil.
- CThe condition of the spark plugs.
- DThe triggering signal from the ignition module or engine control unit (ECU).
Show answer & explanationAnswer & explanation
Correct answer: D. The triggering signal from the ignition module or engine control unit (ECU).
If battery voltage is present at the coil's positive terminal, the power supply to the coil is good. The next step is to determine if the coil is being commanded to fire. This involves checking the ground-side switching (triggering signal) from the ignition module or ECU.
Why the other options are wrong
- A. Spark plug wire resistance is typically checked when there's a weak spark or misfire, not a complete lack of spark when the coil isn't firing.
- B. Checking the coil's primary resistance is a valid test for the coil itself, but without a triggering signal, even a good coil won't fire. The triggering signal should be verified first.
- C. Spark plugs would be checked after confirming spark is being generated by the coil and delivered through the wires.
Ignition System No-Spark Diagnosis
Diagnosing a no-spark condition requires a systematic approach, starting with confirming power to the ignition coil and then checking for the triggering signal.
- No spark means no combustion.
- Check power to coil first.
- Then check for triggering signal (ground-side switch).
Memory trick: No spark? First, 'POWER' it up, then 'TRIGGER' it down.