ASE A1 Engine RepairEngine Electrical Systems (General)Medium
A technician is diagnosing a no-start condition. The engine cranks normally, but there is no spark at the spark plugs. A scan tool shows no Diagnostic Trouble Codes (DTCs). When checking the Crankshaft Position (CKP) sensor, the technician observes a consistent AC voltage signal while cranking. What is the MOST likely cause of the no-spark condition?
- AA clogged catalytic converter.
- BA defective ignition coil or ignition module.
- CA faulty fuel pump relay.
- DLow engine compression.
Show answer & explanationAnswer & explanation
Correct answer: B. A defective ignition coil or ignition module.
If the CKP sensor is providing a consistent signal and the engine cranks, the PCM is aware of engine rotation. No spark with a good CKP signal and no relevant DTCs points towards a failure in the ignition system components (coils, module) that are responsible for generating the spark, or their power/ground.
Why the other options are wrong
- A. A clogged catalytic converter would primarily cause a lack of power or stalling, not a complete no-spark condition during cranking.
- C. A faulty fuel pump relay would cause a lack of fuel, not a lack of spark. The engine would still have spark, but no fuel to ignite.
- D. Low engine compression would affect the engine's ability to run efficiently, but it would not prevent the ignition system from producing spark.
No Spark Diagnosis
Diagnosing a no-spark condition involves verifying the presence of critical engine position signals (CKP, CMP) and then checking the ignition system components responsible for spark generation.
- CKP signal is essential for spark timing.
- Ignition coils/modules generate the high voltage for spark.
- No spark with good CKP points to ignition system failure.
Memory trick: No spark, good crank? Check the 'Ignition Link' for what's gone blank!