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Crankshaft Position Sensor (Crank Sensor / CKP)

Updated: Jan 9

The crankshaft position sensor keeps track of the crankshafts position and rotational speed, it is vital for a smoothly running engine.

In this article, we'll discuss what the crankshaft sensor is, how it works, and what it does.


Table of Contents:

diagram of a crankshaft position sensor

What Is a Crankshaft Position Sensor?

An electrical device called a crankshaft position sensor or crank sensor (CKP) is used in internal combustion engines (petrol and diesel), to keep track of the crankshaft's location and rotational speed.

The crankshaft position sensor is positioned such that the sensor tip passes near to the teeth on the reluctor ring connected to the crankshaft. To provide the engine computer (PCM) a reference point for the crankshaft position, the reluctor ring has one or more teeth missing.

The sensor generates a pulsed voltage signal with each pulse corresponding to a tooth on the reluctor ring as the crankshaft turns.

The engine control unit (ECU) uses this data to regulate the timing of the ignition system, fuel injection, and other engine functions. The crankshaft position sensor, when combined with the camshaft position sensor, enables the engine to be completely in sync and run smoothly.

This is especially important in engines with variable valve timing. When a four-stroke engine starts, this sensor is essential to "synchronise" the engine, giving the ECU the information it needs to know when to inject fuel.

Crankshaft sensors help optimise the engine performance and operation by providing the fuel injection and ignition timing a reference point.

A crankshaft position sensor is often used as the main reference point for determining engine speed in revolutions per minute (RPM).

Prior to the development of electronic crank sensors, petrol engines required the distributor to be manually adjusted to a timing mark.

Types of Crankshaft Sensor

There are different types of crankshaft position sensors, some of the common ones include the following types.

  • Inductive sensor

  • Hall Effect sensor

  • Magnetoresistive sensor

  • Optical sensor

crankshaft position sensor diagram and a number of different types of crankshaft sensors

The most basic sensors are inductive ones, which are often entirely passive electronics.

Compared to inductive sensors, hall effect and magnetoresistive sensors can detect static (non-changing) magnetic fields. Although they are not very durable, optical sensors are able to deliver the most accurate detection.

  • A two-pin connection is seen on pick-up coil type sensors.

  • A three-pin connection is used for the Hall-effect sensor (reference voltage, ground and signal).

The "three-wire" inductive crank sensor is one example of a design element where the third wire is essentially a co-axial shield around the two primary sensor wires to prevent them from picking up stray electrical pulses from elsewhere in the car engine compartment.

Location of the Sensor

The primary crank pulley, the flywheel, the camshaft, or more commonly the crankshaft itself are common places for installation.

Crankshaft position sensors are usually located at the bottom of the engine (primary crank pulley, flywheel and crankshaft) or by the top of the engine by the timing cover (camshaft). It has a distinct appearance.

Failed Crankshaft Position Sensor

A failed crank sensor has many symptoms, it can result in an engine not starting or cutting out while running since the fuel injection (for diesel engines) or spark ignition (for petrol engines) are often timed from the crank sensor position signal.

When it goes wrong, it ceases to send the signal that carries the crucial information for the ignition and other system components.

It can result in the following symptoms:

  • Illumination of the check engine light (CEL)

  • Reduced engine performance

  • Worsened fuel efficiency

  • Difficulty starting the engine

  • Rough idle and increased vibrations

  • Shuddering, shaking and jerking

  • Stalling

  • Misfiring

This sensor also provides speed information to the engine speed gauge (RPM) meaning you may see a slight shift in RPMs or a difference to what you would expect.

The most common OBD fault code related to the crankshaft position sensor is a P0335 code.