How a Crankshaft Position Sensor Works

A crankshaft sitting on a workbench surrounded by tools.

The crankshaft position sensor is a vital electronic device located in the engine of a car. Its purpose is to register the rate at which the crankshaft spins. The engine control unit (ECU) then makes use of this information to regulate ignition and fuel injection. The location of the crankshaft is crucial to how effectively it can gather data. It is situated next to the camshaft belt or the crankshaft. Steel pegs or pins of different widths are arranged around the crankshaft at regular intervals. A powerful magnet is also found next to the crankshaft.

Sensing Function

The magnet radiates a steady magnetic field. When the crankshaft spins, the steel pins are rotated in the magnetic field. This results in fluctuations in the magnetic field. This yields an alternating current (AC) signal, which the engine management unit (EMU) uses to calculate the speed of rotation. The EMU is a type of engine computer. The magnetic oscillation is useful in determining the speed and position of the crankshaft.

Irregular Pin Arrangement

Sometimes a pin may be absent at two consecutive intervals on the crankshaft. Double pins may also occur on the crankshaft. This arrangement varies according to the model of vehicle. The spot with absent pins is referred to as the Top Dead Center (TDC). This results in a signal change at the TDC. The TDC is the primary reference point for various engine timing measurements. Camshaft and ignition timing is determined from here. The TDC also regulates timing of clearance from the pistons to the valves.

When the crankshaft spins, missing or double pins cause fluctuations in the signal at these points. The information is returned to the EMU with regard to the TDC position. The voltage of the peak-to-peak speed signal changes according to engine speed. Faster rotations give rise to increased voltage. When the engine is idle, voltage may be as low as 10 volts, but exceed 100 volts when on high speed.

Analog-Digital Conversions

As a computer, the EMU operates on digital mode. However, the crank sensor is analog, which creates incompatibility. The EMU must use an Analog-Digital Converter to convert the AC pulse into a digital signal.

A Faulty Crankshaft Position Sensor

To enable high engine performance the crank sensor must always be in top shape. A defective sensor will send incorrect data to the EMU. This causes the engine not to perform satisfactorily. It may even cause your vehicle to stall. In the absence of a properly performing crank sensor, the EMU may rely on memory to enable proper ignition and fueling.

However, this is only a temporary backup phase. This is because the crank sensor transmits live data, which is more useful than the static data stored in the EMU. Your vehicle will still work, although performance will be unsatisfactory. It becomes necessary to use electronic measuring equipment to determine the condition of the crankshaft sensor.

A worn out or defective sensor must be replaced to regain proper engine performance. If this is the case, you will need to consult a mechanic.