Crankshaft Position Sensor: What Is It and How It Works

The crankshaft position sensor is a device that gauges the rotation speed and the exact positioning of the engine crankshaft. Without a crankshaft position (CKP) sensor, your car engine would not work.

The crankshaft sensor is installed very close to the central pulley in some cars, while in other cars, the crankshaft sensor is installed in the engine cylinder block or at the transmission bell housing.

The crankshaft position sensor is available in all modern vehicles. It is an important component that is been used to monitor the crankshaft’s rotational position and speed. Also, it sends reports to the engine's control unit to make adjustments should there be any form of malfunctioning. Let's learn more about how it works and how you can replace it in case you ever need that.

How the Crankshaft Position Sensor Works

The CKP sensor is a device that is been used to affirm the rotation of the crankshaft as the engine is moving while giving feedback in form of data back to the main computer. Depending on the design of the manufacturer, the sensor is mainly positioned near the flywheel, engine block, or crankshaft. An electric pulse chart is created as the crankshaft spins and this alters the speed of the engine.

This wavelength regulates the computer output circuits like the ignition timing adjustments, camshaft, and fuel injector pulse width. The sensor makes use of the stator wheel or reflector that is been fastened to the crankshaft.

Symptoms like engine not starting, intermittent stalling, and random misfiring can be a great indication that a sensor is starting to fail. Most times, after been allowed to cool down, the sensor will start work again. It might be difficult for some computer-controlled systems to detect a failing crank sensor due to other genuine reasons that can stop an engine from running, reasons like the sudden engagement of clutch which can cause stalling.

A CKP sensor makes use of a magnetic coil placed in a plastic housing while providing an electrical connector to transmit data to the computer. This sensor is also used by the computer to compile misfiring data because of the temporal deceleration of the crankshaft while the misfire occurs. When the starter is engaged, the computer makes use of the CKP sensor to ascertain that the engine is cranking over.

Then, once the confirmation has been received, the computer will send signals to various sections such as the ignition system and the fuel pump, informing them that the engine is ready to start. If you want to learn more about the knock sensor, check out our other blog post here.

Signs of a Failing Crankshaft Position Sensor

A sensor that is failing can cause irregular problems. A car would stall or cut out randomly while some other time, it would start without any problem. The engine during wet weather might have challenges starting and after a while start perfectly fine.

Sometimes, the motion speed gauge behaves erratically and in some cases, the sensor can result in a long cranking time before the engine starts. There are also times when the engine will crank but will not start at all. These are some signs of a failing CKP sensor. Below are the common symptoms of a failing CKP sensor:

Your “check engine” light comes on

The “check engine” light staying on is one of the popular sign of a bad or failing CKP sensor. Sometimes, overheating can be the cause the check light engine to staying on, in that case, all you need to do is let the engine cool down and it will in turn also cool off the sensor and turn off the light.

So, the check engine light can come on for various reasons, but when it remains on, it is a must you get a professional to check it and point out that is wrong.

Difficulty in starting your car

Difficulty in getting a vehicle to start is another red flag to a failing CKP sensor. When there is an attempt to starting a vehicle, the CKP sensor immediately starts to monitor the speed and position of the crankshaft. So, if the sensor is having any problem, this process will cease to commence and it will result in the engine not turning on at all.

Backfiring/stalling of your vehicle

Along with the same lines with the symptom above, a faulty crankshaft position sensor can cause a vehicle to backfire and/or stall. Stalling is a more popular problem in a vehicle than backfiring, as the interference of the crankshaft signal can result in the engine getting off. Backfiring can occur depending on the length of time the signal has been out and also depending on the car's speed at the tune it occurs.

When the engine is making your vehicle vibrate

Another symptom of a bad CKP sensor is an obvious vibrating protruding from the engine. There are speculations that there is always a bit of vibration coming from the engine when it is running. But, if there is an intense increase in the vibrations, it is mostly possible that there is a problem with the CPK sensor.

Also, the vibrating often comes paired with intense drop-in power and fuel economy, and this will result in the car needing more gas and power to move.

Slow response from the accelerator

If there is any problem with the sensor, it won't send a piece of valid information regarding the positioning of the cylinder. This means that there will be space between the computer obtaining information and applying it. As a result of this, the accelerator hesitates and doesn't give a definite response.

Cylinder misfiring

Cylinder misfiring is also a very common sign to watch out for when a car is experiencing some crankshaft position sensor problems. A failing sensor cannot give a piece of correct information about the position of the piston, and this will result in one of the cylinders misfiring.

Although, if there is an issue with the spark plug, it will draw the same response of having a misfiring cylinder problem, but if the problem persists after checking the spark plug and other things that might be the cause of the problem, then the CPK sensor may be the culprit.

How to Test a Crankshaft Position Sensor

Depending on a particular vehicle model or make, a bad or a failing CKP sensor can produce one or more of the symptoms mentioned above. However, there are problems in other systems of a car, such as the ignition or the fuel systems, that can also make a car produce some of the symptoms listed above.

This is why it is very important to make sure a CKP sensor is tested so that the real problem can be identified. It is often recommended to test a crankshaft position sensor using an oscilloscope; although, an oscilloscope is not a common tool for car owners. You can also use a digital multimeter (DMM) to troubleshoot your sensor without minding whether your engine uses a hall effect type sensor or an inductive one.

You will need the crankshaft position sensor electrical values for a particular vehicle's model and make, and there will be a need for you to locate the sensor, identify wires, and if it is necessary, replace it. Keep in mind that more information can be found in the vehicle's repair manual.

Troubleshooting a Crankshaft Position Sensor

Many problems with the crankshaft position sensor can be found on the sensor's connector or the wiring harness. So ensure that you carefully examine them before you start to troubleshoot the sensor itself. But the first and most important step is to locate the sensor. Depending on the vehicle make and model, you can locate the CKP sensor, which is:

Mounted on the engine's timing or front cover, behind the harmonic balancer, or very near to the crankshaft pulley.
Located around the middle of the engine block.
Right under the starter motor.
on the back of the engine, at the bell housing of the transaxle, very near to the flywheel ring gear.

Checking the Wiring and Sensor

Most times, a failing sensor is caused by a bad connector or wire. So, it is important to make a visual examination of the connectors or harness between the sensor or ignition module.

Examine the wires for any damage
Scan for loose wires
Inspect for detached sensor mounting bolts
Examine the electrical connector for damage
Test the sensor itself for indications of damage

Make sure to check out the video if you want to learn more about this:

How to Test an Inductive Type CKP Sensor

The inductive (also called magnetic) CKP sensor has the following features:

It has one or two wires.
Additionally, it produced its own alternate current voltage signal
It is mounted in front of a reluctor wheel or rotor.

To test an inductive type CKP sensor, use the steps highlighted below:

Unplug the crankshaft position sensor electrical connector.
Fix your digital multimeter to direct current voltage using a low range.
Don't start the engine yet, but ensure the ignition is on.
Touch the ground with the digital multimeter black. It can be a neat surface on the engine.
On the strap of the connector you unplugged, touch the digital multimeter red lead to each of the sensors. One of the wires should generate around 1.5 volts; if not, then it means the sensor is not earning enough voltage and thus needs to be fixed.
To hinder the engine from starting, you can disable it by removing the relay or fuel pump fuse. Better still, detach the ignition cable between the distributor and ignition coil.
Fix your digital voltmeter to a low range on the alternate current voltage scale.
Attach your sensor pin to the meter leads. During the test, ensure that you keep your meter lead wires away from moving parts of the engine.
For some few seconds, crank the engine and watch the meter's readout.
By now the sensor should generate a voltage pulsing signal. And if you don't see any, replace the sensor.

How to Test a Hall Effect Type CKP Sensor

The features of hall effect CKP sensors are:

Has up to three or four wires
Mounted in front of a reluctor wheel or rotor
Generates a digital (square wave) signal
Requires an external power source and a ground to generate the signal.

To test a hall effect type CKP sensor, use the steps highlighted below:

During the test, make sure you remove the relay or fuel pump to deter the engine from starting. If the engine makes use of a distributor, simply unplug the ignition cable and set it on the engine making use of a jumper wire.
Unplug the crankshaft position sensor electrical connector.
Put your digital multimeter to direct current volts within a range of 20 Volts.
Touch the digital multimeter black lead to the black wire on the strap connector.
Touch the digital multimeter red lead to the red wire on the strap connector.
Turn on the ignition key, but don start the engine yet.
Depending on the car make and model, by now, your meter should display data between 5 to 13 volts. If the voltage is zero or lower than what you expected, you can freely check the connector and wire for damage
Turn off the ignition and plug back the crankshaft position sensor to the harness connector.
Fix your digital multimeter to a low direct current voltage to enable the reading of the millivolts.
Touch the digital multimeter black lead to battery negative.
For a few seconds, crank the engine; your digital multimeter should register about 200mv-300mv.
Touch your digital multimeter red lead to the green wire on the harness connector.
For another few seconds, crank the engine and your meter should read around 300mv which is the average voltage of the signal the crankshaft position sensor generates.

If you need to test the knock sensor, make sure to check out this blog post.

Replacing the Crankshaft Position Sensor

Replacing a CKP sensor is a simple operation. But, on some car models, there may be a need to remove one or more components to be able to access the sensor.

Ensure the engine is cool and the ignition switch is off
Detach the negative terminal from the battery.
For some models, there might be a need to lift the front of the vehicle and solidify it safely on a jack stand, to able to gain access to the sensor.
Unplug the crankshaft position sensor electrical connector.
Lose the mounting bolt(s).
Bring out the sensor from the engine.
If the sensor comes with an O-ring, grease it with a light coat of oil before installing the sensor. This will assist the sensor to seat correctly, and generate an accurate signal, and also prevents oil leaks.
Install the new sensor and fasten the mounting bolts.
Plug the sensor electrical connector and attach the negative term into the battery.

By the way, when replacing the CKP sensor make sure to check out the brake disc, here is another blog post that covers that topic in more details.

Final Thoughts

There are various names given to the crankshaft position sensor, depending on the choice of the manufacturer, some call it CKP sensor, some call it crankshaft angle sensor, and others call it as we do - crankshaft position sensor.

However, they all perform the same functions irrespective of their different names. It is used to monitor the crankshaft’s rotational position and speed and just like any part of the car, it sometimes can get broken. Hopefully, this blog post helped you to learn more about the importance of this car component and what you should do you spot some malfunction.

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