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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.

Causes of Sensor Failure

The sensor may sometimes burn out, get worn out, or just fail at a high mileage (usually over 80,000 miles).

Exposure to heat (such as if an engine overheats) is a potential factor in sensor failure. Other causes include rust on the pins of connectors or vibration that damages a wire.

Since many modern crankshaft sensors are sealed, water or other liquids cannot affect them.

If a crankshaft position sensor is replaced it should be relearned to avoid issues.

Can a Car Start With a Bad Crankshaft Sensor?

If the crankshaft sensor is not working correctly, it is likely that a vehicle will not start. This is because the sensor sends electrical signals to the ECU, or engine control unit, indicating the position and speed of the crankshaft.

These signals are crucial for proper ignition timing and fuel injection. Without them, the engine may struggle to start or may start but then stall shortly after.

However, there are instances where a car may still be able to start even with a faulty crankshaft sensor.

For example, if the sensor is only partially damaged, it may still be able to provide some signals to the ECU. This may allow the car to start and run for a short period, but it may also result in the car stalling or experiencing reduced performance and fuel efficiency.

There may be ways to start a car if the crankshaft sensor is faulty but it's best to have the sensor replaced if it fails.

What Happens if You Don’t Fix a Bad Crank Sensor

Failing to address a malfunctioning crankshaft sensor can have serious consequences for your vehicle. The sensor plays a vital role in the proper functioning of the engine, and a faulty sensor can lead to a range of issues that can impact the performance and reliability of your car.

If left unchecked, a bad crankshaft sensor can even cause engine damage if you continue to drive the vehicle.

Ignoring a malfunctioning crankshaft sensor can result in a no-start situation, leading to a breakdown on the road. This not only inconvenient, but it can also be dangerous if you are stranded in a remote location or on a busy road.

In addition to these issues, it may be illegal to drive a vehicle with a failing crankshaft sensor due to increased emissions. If the sensor is not working properly, it can result in the engine running less efficiently, which can lead to higher emissions and potentially violate emissions regulations.

To avoid these problems and ensure the safe and reliable operation of your vehicle, it is important to address any issues with the crankshaft sensor as soon as they are detected and replace the crankshaft sensor if needed.


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