What is a Crank Sensor? What Does it do? Where is it Located?

The crankshaft position sensor (CKP sensor or CPS) is one of several sensors that keep your engine running smoothly. It measures the position of the crankshaft (for which it is sometimes called the crank angle sensor or CAS), as well as the rotational speed of the crankshaft (for which it is sometimes called the engine speed sensor, ESS, or the RPM sensor). The crankshaft position sensor relays this information to the vehicle's onboard computer, the engine control unit (ECU). The ECU uses that info, along with inputs from other sensors, to control systems like ignition timing and fuel injection. This keeps all the parts of the engine well timed and working in concert. The crankshaft position sensor is essential to a smooth-operating engine. 

How Does the Crank Sensor Work, Exactly?

There are different setups for crankshaft sensors, but they tend to work on principles of magnetism. Many crankshaft position sensors are a type of electronic sensor known as a Hall effect sensor. A Hall effect sensor produces electricity in when it is exposed to a magnetic field. In a crankshaft position sensor, a toothed wheel, spinning with the crankshaft, disrupts the magnetic field. That produces a pattern of on and off switches in the Hall Sensor that the ECU can interpret as the crankshaft speed. The faster the sensor is turning on and off, the faster the crankshaft is spinning.

While these Hall effect sensors give a digital signal, some crankshaft position sensors produce an analog signal. They still operate on magnetism, though. The sensor produces an electrical voltage based on fluctuations in a magnetic field. The fluctuations are caused by the movement of metal pins in the crankshaft. Faster spinning means more fluctuations, means more voltage. The ECU is able to translate this voltage into crankshaft speed.

In either case, the timing elements, the pins or the teeth on the wheel have to be evenly spaced to convey an accurate measure of speed. There is usually a gap though, which matches when one piston is at top dead center. This gap allows the sensor to determine where the crankshaft is in its rotation in addition to its speed.

Where is the Crankshaft Position Sensor Located?

The location of the crankshaft position sensor can vary from one vehicle to another. Obviously it must be close to the crankshaft, so it is most often located on the front underside of the engine. It can usually be found mounted to the timing cover. Sometimes it may be mounted at the rear or the side of the engine. Sometimes the crankshaft position sensor measures the speed of the clutch flywheel to determine the speed of the crankshaft. In these cases, the sensor is mounted to the bell housing of the transmission.

Like with most parts, crankshaft position sensors can eventually fail for a variety reasons. To learn more about what those reasons are, check out this article about why crankshaft position sensors fail from the experts at 1A Auto!

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