Crankshaft position sensor (CKP): how it works, symptoms and problems

Vehicles are made up of numerous parts with numerous functions. Every component is essential and should not be neglected for the excellent functioning of your car. The Crankshaft Position Sensor is vital for your vehicle’s adequate functioning, and this article aims to shed light on it.

You might not have paid attention to this part of your car, or you might have, but not what it is called; whichever category you fall under, this article is a crankshaft sensor guide for you, and you are assured of good insight.

What is a Crankshaft Position Sensor?

Before understanding what a Crankshaft Position Sensor is, it is not out of place to know what a crankshaft is. This makes understanding a Crankshaft position pretty much more effortless.

A Crankshaft is the backbone of the internal combustion engine. This means that it is responsible for the engine’s proper functioning and converting linear motion to rotational motion. In other terms, the Crankshaft is the moving portion of the internal combustion engine.

Another critical function of the Crankshaft is to transmit power to other engine systems, including oil pumps, air conditioning compressors, valve timing, and alternator, among others.

In simple terms, a Crankshaft Position sensor is an electronic device used in a combustion engine (internal) and monitors the Crankshaft’s rotational speed or position. The crankshaft position sensor determines the speed of rotation and the specific position of a crankshaft. Without a Crankshaft Position Sensor, your vehicle’s engine can’t start; it is that important. It is also known as the Crankshaft Angle Sensor or the Crankshaft Speed Sensor. The Crankshaft Position Sensor has been abbreviated to CKP.

Where Is The Crankshaft Position Sensor Located?

It has been established that the Crankshaft Position Sensor is located in the internal combustion engine; however, there are more specifics as to where it is located. It is worthy of note that it is not found in the same place in every car.

In some cars, the Crankshaft Position Sensor is located close to the main pulley, also known as a harmonic balancer. In other vehicles, it can be installed in the engine cylinder block or at the transmission bell housing, as the case may be.

The CKP is positioned so that the teeth on the reluctor ring joined to the Crankshaft pass close to the sensor tip. The reluctor ring provides the engine computer with the point of reference to the Crankshaft position. This explains why it has one or more teeth missing.

Functions of the Crankshaft Position Sensor

Apart from the fact that the Crankshaft Position Sensor monitors the Crankshaft’s rotational speed or position, it has some other functions. They include:

  • It informs the Electronic Control Unit (ECU) of the exact position of the Crankshaft.
  • Decides optimal fuel injection and regulates ignition.
  • The Crankshaft Position Sensor monitors the location of the camshaft.
  • It uses the information it can gather to optimize the injection of fuel into the engine of a vehicle.
  • The Crankshaft Position Sensor ensures that the engine performs at an optimum level. It also adds to the engine’s efficiency.

How does the Crankshaft Position Sensor Function?

A toothed wheel, known as the reluctor ring, attached to the rotating Crankshaft breaks up a magnetic field as it passes the sensor. This is to determine the specific position of the Crankshaft.

More often than not, the reluctor wheel has six slots set 60 degrees apart from each other, and a seventh slot is placed 10 degrees from one of the others. The seventh slot is used to provide an extra pulse of synchronization every time the wheel revolves.

Under exceptional circumstances, the reluctor ring can have up to 360 teeth; each teeth represents a degree of Crankshaft rotation. As the reluctor ring is responsible for generating pulses, the Crankshaft Speed Sensor is tasked with transmitting signals to the ECU to be processed.

As the Crankshaft rotates, the sensor produces a pulsed voltage signal, and each pulse corresponds to the tooth on the reluctor wheel. The PCM makes use of the signal from the CKP to determine what time the spark should be produced, and in which cylinder.

The signal that comes from the Crankshaft Position Sensor is also used to monitor any of the cylinders’ misfiring. There will be no spark in the absence of any signal from the sensor; consequently, the fuel injections will not work.

The two most common types of sensors are:

  • The magnetic sensors: Which have a pick-up coil that produces A/C voltage (has a two-pin connector).
  • Hall-effect sensors: which produce a digital square wave signal (has a three-pin connector: Reference voltage, ground and signal).

The Most Common Problems of the Crankshaft Position Sensor

Several reasons are responsible for the problems of the CKP; however, these problems, more often than not, manifest themselves in engine timing. This makes a precise diagnosis pretty tricky.

To make the fault-finding process easier, it is crucial to begin with the most common problems and their respective symptoms.

Few things affect the Crankshaft Position Sensor apart from the obvious issues (electro-mechanical failure or a wiring problem).

Some of the common problems include but are not limited to:

  • The accumulation of oil and dirt on the tip of the sensor.
  • A wrong alignment of the mounting bracket of the sensor.
  • A damaged reluctor ring.
  • A bad flex plate.

Pointers to Crankshaft Position Sensor Problems

The most obvious pointer to a CKP problem is an engine that won’t start. There are other things to look out for to know whether a Crankshaft Position Sensor is faulty or not. These pointers include but are not limited to:

  • Engine misfire
  • Engine stalling
  • No extinguishing from the engine check light
  • Rough idle
  • An increase in fuel consumption.

Testing the CKP

Before proceeding to test the CKP of your vehicle, ensure that you thoroughly inspect it for loose or corroded pins, cracks, or other evident damages. The sensor tip should also be inspected to be sure that it is clean and that the air gap maintains the manufacturer’s specification.

For the pick-up coil sensors: The testing process includes checking the resistance. For instance, for the 2008 Ford Escape, the resistance of the CKP should be between 250-1,000 ohms. If the resistance is lower or higher than the specified range, then it must be changed.

For the hall-type sensors: The reference voltage and the earth signal must be tested. The best way to check a CKP signal is by making use of an Oscilloscope.

At times, the sensor may have a fault that is intermittent and not present in the process of testing; at such times, going through Technical Service Bulletins (TSBs) comes in handy. The CKP can be checked with a scan tool. This scan tool reveals the sensor signal.

Source: Car Care and Maintenance Blog

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