Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairMedium
A vehicle with a distributor-type ignition system is experiencing a no-start condition. The technician confirms that the ignition coil is receiving battery voltage on its primary positive terminal when the key is in the 'RUN' and 'START' positions. However, there is no spark at the spark plugs. What component should the technician investigate next to determine why the primary circuit is not being switched (grounded) to induce a spark?
- AThe secondary winding resistance of the ignition coil.
- BThe spark plug wires for excessive resistance.
- CThe ignition control module (ICM) or equivalent switching device.
- DThe condition of the rotor and distributor cap.
Show answer & explanationAnswer & explanation
Correct answer: C. The ignition control module (ICM) or equivalent switching device.
If the primary coil is receiving power but not switching on and off (meaning no spark), the component responsible for performing that switching action in a distributor-type system is the ignition control module (ICM) or a similar electronic switching device. This module grounds and ungrounds the primary circuit based on signals from the crankshaft or camshaft position sensors.
Why the other options are wrong
- A. Secondary winding resistance is also part of the secondary circuit and wouldn't prevent the primary circuit from switching.
- B. Spark plug wires are part of the secondary circuit and would only be an issue if there was a spark trying to get through.
- D. Rotor and distributor cap are secondary components; they distribute the spark, but don't generate it.
Ignition Control Module (ICM)
An electronic component in distributor-type ignition systems responsible for switching the primary current of the ignition coil on and off to induce high voltage.
- Receives signals from engine sensors.
- Controls primary coil current.
- Failure leads to no-spark or misfire.
Memory trick: The 'brain' (ICM) tells the 'heart' (coil) when to beat (spark).