Autonatomy | CKP & CMP Lab

Learning objective

Explain why the crankshaft position (CKP) signal provides engine speed and angular reference, while the camshaft position (CMP) signal helps identify engine-cycle phase. Compare normal signals with a missing signal or shifted cam reference.

Simplified four-stroke engine with a 12-1 crank pattern and one cam pulse per 720° cycle. Real vehicles use different tooth patterns, sensor technologies, signal levels, sync strategies, and fault responses. The display is conceptual, not an OEM oscilloscope capture.

1 · Operate the engine

Engine speed: 1200 RPMSensor conditionInspect crank angle: 0°

The crank rotates twice (720°) while the cam rotates once (360°). The missing-tooth gap repeats each crank revolution; the cam reference distinguishes the two revolutions.

2 · The Challenger

The CKP pattern is present and engine RPM is detected, but the CMP signal is absent. Which conclusion is supported?

Choose oneCrank speed can still be detected; the ECM may have difficulty identifying cycle phase, depending on its strategy.The crankshaft is mechanically stopped.The timing chain is definitely broken.

Select an answer to test your reasoning.

3 · Two-revolution scope

Detected CKP RPM—

CKP reference—

CMP reference—

Cycle synchronization—

Crank angle—

Cam angle—

4 · Technician's reasoning

A missing CMP signal does not, by itself, prove incorrect mechanical valve timing. A shifted cam reference is a correlation clue, not proof of a stretched chain: inspect the sensor circuits, reference pattern, and vehicle-specific service information before diagnosing a mechanical fault.