Crankshaft Position Sensor

It reads a toothed reluctor wheel on the crankshaft or flywheel, usually with one or two missing teeth as a reference mark. From the pulses the control unit calculates engine speed and the exact position of every piston. Sensors are either inductive (generating their own AC signal) or Hall-effect (switching a supplied voltage). The signal is also used to detect misfires: a cylinder that does not fire causes a tiny slowdown in crankshaft speed.

The sensor reads a toothed reluctor wheel, often with one or two missing teeth that mark a reference position. Inductive and Hall-effect designs are both common.

Each tooth passing the sensor produces a pulse. The gap marks a known position; counting teeth from there gives the crank angle at any moment. From the timing of the teeth, the control unit calculates both engine speed and the exact crankshaft angle, which it needs to time each spark and injection.

A failing sensor often causes sudden stalling, especially when hot, and a no-start with a normally cranking engine. P0335 is the typical code; the rev counter may also drop to zero while cranking. Failing sensors often cause stalling when hot, then starting again after cooling down. A tachometer that does not move while cranking is a useful clue that the signal is missing.