Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairMedium
A client complains that their vehicle intermittently stalls and has a 'check engine' light illuminated. A technician retrieves diagnostic trouble code P0340, indicating a Camshaft Position Sensor (CMP) Circuit Malfunction. Which of the following is the MOST likely impact of a failing CMP sensor on the ignition system?
- AReduced spark intensity due to low voltage.
- BIncorrect ignition timing or no spark.
- CPremature spark plug wear.
- DIncreased primary coil resistance.
Show answer & explanationAnswer & explanation
Correct answer: B. Incorrect ignition timing or no spark.
The Camshaft Position Sensor (CMP) provides the Engine Control Module (ECM) with information about the camshaft's position, which is crucial for determining the correct cylinder firing order and thus precise ignition timing. A faulty CMP sensor can lead to incorrect timing or a complete loss of spark if the ECM cannot synchronize ignition events.
Why the other options are wrong
- A. Reduced spark intensity is typically related to coil or power supply issues, not directly a CMP sensor.
- C. Premature spark plug wear is usually caused by conditions like overheating, fouling, or incorrect gap, not directly a CMP sensor failure.
- D. Primary coil resistance is a characteristic of the coil itself and not directly influenced by sensor input.
Camshaft Position Sensor (CMP) Function
The CMP sensor monitors the camshaft's rotational position, providing crucial data to the ECM for accurate ignition timing and fuel injection synchronization.
- Works with the Crankshaft Position Sensor (CKP) for engine synchronization.
- Its signal helps the ECM determine which cylinder is at its compression stroke.
- A faulty CMP can cause misfires, no-start conditions, or stalling due to incorrect ignition/fuel timing.
Memory trick: CMP knows the cam, CKP knows the crank; together, they time the engine.