What Is a Crank Sensor?

Updated February 21, 2017

The crank sensor is a tiny, yet important part in the modern internal combustion engine. Developed to work with emerging electrical and computer-based systems, the crank sensor is ubiquitous to automotive construction. It's a component that when working properly is barely noticed, but when a malfunction occurs it can impact fuel economy, ignition and acceleration performance.


As the internal combustion engine was innovated its complexities grew. New electrical components demanded a monitoring system so all parts could be evaluated in real time for performance and regulation. The crank sensor (also called crankshaft sensor) is one such electrical component of the modern-day internal combustion engine. It monitors the rotational speed or position of the crankshaft so it no longer must be inspected manually (by a mechanic) but is monitored by the automobile's on-board computer.


The more moving parts an internal combustion engine has, the greater the need to make certain all parts are working in accordance with one another. The crank sensor allows for more complex engine construction such as variable valve timing and fuel injection systems. "The CAS [crank sensor] is an inductive signal generator; it measures reluctance," writes, a publication compiled from the experience of auto mechanics. "The CAS is typicality found on injection engines, and it's an important sensor. Without it, the engine will not run at its optimum, and if faulty, the ECU warning light shall illuminate on the dash."


The crank sensor is usually found adjacent to the cam belt or the crank shaft itself. A magnet acts as the signal generator, creating a magnetic field. This enables the fly wheel to spin and the pins or pegs of the camshaft to turn. The automobile's engine management units (computer system) uses this information to calculate the speed of the rotation via the crank sensor. Without these measurements the engine's timing could be thrown off very quickly and the resulting repair bill would be expensive.


There are many variations on the crank sensor just as there are many models of the internal combustion engine. The part is relatively cheap to purchase compared to other engine components but that is not to say the part is not integral. The internal combustion engine depends on timing to work properly, and without the crank sensor timing is difficult to manage. A form of crank sensor is also used on bicycles to monitor rotational speed and position of the crank set.


The crank sensor allows the engine to work at optimal performance. It creates better fuel economy, ignition and acceleration by correctly monitoring the timing and speed of the engine's integral components. Because of this, the sensor should be checked (along with other moving parts) every six months to ensure the car is working properly and at its peak.

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About the Author

Jonathan Lister has been a writer and content marketer since 2003. His latest book publication, "Bullet, a Demos City Novel" is forthcoming from J Taylor Publishing in June 2014. He holds a Bachelor of Arts in English from Shippensburg University and a Master of Fine Arts in writing and poetics from Naropa University.