ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Easy
A technician is diagnosing a vehicle that cranks normally but will not start. They perform a basic check and confirm there is no spark at any of the spark plugs. Which of the following components should be tested first as a common cause for a no-spark condition affecting all cylinders?
- AFuel injectors
- BCrankshaft Position Sensor (CKP)
- CIgnition coils
- DSpark plugs
Show answer & explanationAnswer & explanation
Correct answer: B. Crankshaft Position Sensor (CKP)
A crankshaft position sensor (CKP) is crucial for the engine control module (ECM) to determine engine speed and position, which is essential for timing both fuel injection and ignition. If the CKP sensor fails, the ECM will not know when to fire the ignition coils, resulting in a no-spark condition across all cylinders.
Why the other options are wrong
- A. Fuel injectors are responsible for fuel delivery, not spark production, and would cause a no-fuel, not a no-spark, condition.
- C. Multiple ignition coils failing simultaneously is unlikely; a single coil failure would affect only one or two cylinders.
- D. Faulty spark plugs would typically cause misfires or rough running, not a complete no-spark condition for all cylinders.
Crankshaft Position Sensor (CKP)
An electronic device used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by the engine control module (ECM) to control ignition timing and fuel injection.
- Essential for engine timing (spark and fuel).
- A common cause of no-start conditions, especially no-spark.
- Typically a magnetic pickup or Hall effect sensor.
Memory trick: When the crank sensor's gone, no spark will be shown.