Understanding crankshaft position sensor

The crankshaft and camshaft position sensors, which are the most significant sensors in any engine, are critical to the distributor’s and ignition timing’s performance. The crankshaft position sensor is a multipurpose sensor that controls ignition timing, detects RPM, and calculates relative engine speed. Manual distributor timing is no longer necessary thanks to this sensor. To synchronize the fuel injector and coil firing sequence, the camshaft position sensor is employed to detect which cylinder is firing.

In today’s article, you’ll learn the definition, functions, diagram, types, working, and common symptoms of a crankshaft position sensor.

Crankshaft position sensor

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What is a crankshaft position sensor?

Crank sensors are electronic devices that monitor the position or rotational speed of the crankshaft in internal combustion engines, both gasoline, and diesel. Engine management systems employ this data to adjust the timing of fuel injection and other engine characteristics. The distributor had to be manually set to a timing mark on petrol engines until electronic crank sensors were available.

The crank sensor can be used in conjunction with a camshaft position sensor to monitor the engine’s piston-valve relationship, which is especially significant in engines with variable valve timing. This procedure is also used to “synchronize” a four-stroke engine when it first starts, allowing the management system to determine when to inject gasoline. It is also widely used to determine engine speed in revolutions per minute. The main crank pulley, the flywheel, the camshaft, and the crankshaft itself are all common attachment points. This sensor, together with the camshaft position sensor, is one of the two most critical sensors in modern engines.

Because the crank sensor position signal is used to time the fuel injection (diesel engines) or spark ignition (petrol engines), a failed sensor will cause the engine to not start or cut out while running. This sensor also provides speed information to the engine speed indicator.

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The followings are the functions of crankshaft position sensors:

  • The crankshaft position sensor’s primary function is to determine the crank’s position and/or rotational speed (RPM).
  • The information sent by the sensor is used by Engine Adjust Units to control factors such as ignition timing and fuel injection timing.
  •  In diesel engines, the sensor will control the fuel injection.
  • The sensor output may also be linked to other sensor data, such as the cam position, to determine the current combustion cycle, which is critical for a four-stroke engine’s beginning.

The primary functions of a crankshaft position sensor include:


A powerful magnet can be found next to the crankshaft if you look closely. Around the crankshaft, you’ll also notice steel pins or pegs positioned at regular intervals. This magnet emits a continuous magnetic field all of the time. The steel pins around the crankshaft rotate around this field as the engine starts and the crankshaft spins. As a result of the variation in the field, an AC (alternating current) signal is produced. This also instructs the engine management unit (engine computer) to determine the rotational speed. As a result, the EMU can compute the camshaft’s position and speed in order to improve fuel injection and ignition.


We must learn one thing from modern automobiles. Only if the internal parts are moving at a specific required pace will the engines provide us with efficient performance. The onboard computer can only use the information sent to it by the crankshaft position sensor once it detects the rotation of the crankshaft inside the engine. This is when the computer makes little adjustments or fine-tunes to the engine in order to improve its efficiency.

Consider the situations in which you’re going full throttle. The computer needs to make these tiny adjustments to the engine in order to modify the speed in settings like cruise mode or sports mode because the throttle is constant. The computer will make sure that the crankshaft’s rotational speed is constantly monitored, compared to the appropriate range, and speed adjustments are made as needed. This adjustment can be made in terms of both speed increase and speed decrease.

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Elements and diagram of a crankshaft position sensor:


Types of a crankshaft position sensor

the following are the various types of crankshaft position sensors:


in this type of crankshaft position sensor, a magnet is used to detect a signal from the engine cranking. Either in the engine block, close to the flywheel, or close to the crankshaft itself. Notches on a spinning disk, reluctor wheel, or crankshaft are picked up by it. The magnetic field changes as each notch pass, sending an alternating current signal to the ECU.

Hall Effects:

This type is similar to the inductive sensor in that it is positioned in the same locations and responds to the same notches. It creates a digital signal instead of an analog AC signal. As the notches travel by the sensor, it turns on or off.

AC Output Sensor:

The output of an AC output sensor differs from that of other sensors in that it is an AC voltage signal. The exciter coil, which is placed near the rotating disc, receives a very high frequency (between 150 and 2500 cycles per second) from the onboard controller. This disc has a slot in it and is attached at the end of the camshaft. The mutual inductance excites the slot as it goes through the coil, and a signal specifying the position of the first cylinder is sent to the onboard controller. Some Vauxhall ECOTEC engines employ this type of sensor.

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Working Principle

The working of a crankshaft position sensor is less complex and can be easily understood. In its working, the teeth on the reluctor ring attached to the crankshaft pass near to the sensor tip on the crankshaft position sensor. One or more teeth are missing from the reluctor ring, which serves as a reference point for the engine computer (PCM). The sensor generates a pulsed voltage signal when the crankshaft spins, with each pulse corresponding to a tooth on the reluctor ring. With the engine idling, the photo below displays the actual signal from the crankshaft position sensor. As you can see from the graph, the reluctor ring in this vehicle has two missing teeth.

The PCM uses the signal from the crankshaft position sensor to determine when and in which cylinder to fire the spark. The signal from the crankshaft position is also utilized to check for misfires in the cylinders. There will be no spark and the fuel injectors will not operate if the sensor signal is missing.

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Magnetic sensors with a pick-up coil that produce A/C voltage and Hall-effect sensors that produce a digital square wave signal, as shown in the photo above, are the two most prevalent varieties. Hall-effect sensors are used in modern automobiles. A two-pin connector is found on a pick-up coil sensor. A three-pin connector is used to connect the Hall-effect sensor (reference voltage, ground, and signal).

Watch the video below to learn the visual aspect of the working of a crankshaft position sensor:

Symptoms of a bad or failing crankshaft position sensor

The followings are the common problem one encounter when a crankshaft position sensor fails:

Difficult Starting:

Difficulty starting the car is the most prevalent indication of a damaged or failed crankshaft position sensor. The crankshaft position sensor keeps track of the crankshaft’s position and speed, as well as other information that is vital when starting the engine. The car may have intermittent starting troubles or not start at all if the crankshaft position sensor is malfunctioning.

Intermittent Stalling:

Intermittent stalling is another common indication of a malfunctioning crankshaft position sensor. If there is a problem with the crankshaft position sensor or its wiring, the crankshaft signal can be cut off while the engine is operating, causing the engine to stall. This is frequently an indication of a wiring issue. This symptom can potentially be caused by a faulty crankshaft position sensor.

Check Engine Light is on:

An illuminated Check Engine Light is another sign of a possible problem with the crankshaft position sensor. If the computer identifies a problem with the signal from the crankshaft position sensor, the Check Engine Light will illuminate to inform the driver. A Check Engine Light can be triggered by a variety of other problems. It is highly suggested that the computer be inspected for error codes.

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Uneven Acceleration:

The engine control unit is unable to adjust spark timing and fuel injection when the engine speed increases due to erroneous input from the crankshaft position sensor. A lack of accuracy can cause slow or uneven acceleration, making it difficult to maintain a constant pace.

Engine Misfires & Vibrates:

A transient stutter in the engine could be a sign of misfiring cylinders caused by a faulty crankshaft position sensor. When a crankshaft position sensor fails, it is unable to deliver accurate information about piston positioning in the engine, resulting in cylinder misfiring. This could also be caused by improper spark plug timing, but if the spark plug is fine, the crankshaft sensor is the most likely culprit.

Engine Rough Idle and/or Vibrating:

Rough idling is another indicator of a crankshaft position sensor problem. You may detect the motor grinding or vibrating while stopped at a red light or otherwise. When this happens, the sensor isn’t monitoring the position of the crankshaft, resulting in vibrations that reduce overall engine output. The engine’s mileage tracking can also be hampered by the vibration. Any unusual vibrations should be investigated as soon as possible by a mechanic.

Gas mileage is reduced:

Fuel injectors will not properly pump gas into the engine if the crankshaft position sensor does not provide appropriate timing information. On short and long drives, the engine will use more gas than it needs, lowering overall fuel economy. Inspect the sensor with a mechanic, as insufficient fuel economy might be caused by a variety of faults.

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A crank sensor can be used in conjunction with a camshaft position sensor to monitor the engine’s piston-valve relationship, which is especially significant in engines with variable valve timing. This procedure is also used to “synchronize” a four-stroke engine when it first starts, allowing the management system to determine when to inject gasoline. That is all for this article, where the definition, functions, elements and diagram, types, working, and symptoms of bad crankshaft position sensor are been discussed.

I hope you learn a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!