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The Engine Speed Sensor, also known as the Crank Sensor or Crankshaft Sensor, is implemented in a car’s engine to gauge how fast it’s moving. This information is converted to the rev meter on your dashboard to let you know exactly how fast your engine is spinning.
The rev meter measures in rpm, or “revs per minute.” One revolution of the engine happens when the cylinders have fired, and the pistons are back to their positions before the cycle started.
You shouldn’t confuse this with the Transmission Speed Sensors. There are two sensors on your transmission: one on the input shaft and one on the output shaft. These transmit data to the ECU (Electronic Control Unit – the “brain” of the car) to help it choose what gear it should be in at any given moment and measure vehicle speed. Many other articles you see online confuse these sensors. They do work in the same way, but they measure different things.
If something is wrong with your Engine Speed Sensor, it may affect how safely you are driving on the road in various ways – we will go through these a bit later in this article.
In this article, we will look through some of the signs that something’s wrong so that you can get it fixed as soon as possible.
What is an Engine Speed Sensor?
An Engine Speed Sensor is attached to the crankshaft.
In all cars, the sensor is used to ensure that fuel injection and ignition timing happen at the right time.
You’ll find an Engine Speed Sensor on every road-legal car in the USA.
What is a Crankshaft?
The Engine Speed Sensor is attached to the crankshaft. Before going into any detail about this sensor, we should first establish what the crankshaft is if you aren’t familiar with it already.
In your engine, the pistons move up and down in the cylinders, following the almost universal 4-stroke ICE (internal combustion engine) sequence of suck, squeeze, bang, blow. The piston heads are attached to the crankshaft using con rods.
The con rods allow the reciprocating movement of the pistons to translate into rotational energy in the crankshaft. The faster the combustion reactions happen in the cylinders, the more force the pistons will be driven down with, and the greater the speed of the crankshaft will be.
At the end of the crankshaft, you will find the flywheel. This is what connects to your transmission and allows the wheels to turn.
Like all car parts, the crankshaft on one car is designed differently to another car’s crank.
How Does an Engine Speed Sensor Work?
Like most sensors you find in cars, the Engine Speed Sensor is very simple. It works by utilizing the principle of electromagnetism.
A toothed metal disc is attached to the crankshaft in the car. You will also find an electromagnetic coil and a signal receiver, and these devices are stationary.
The toothed metal disc is attached directly to the crankshaft and spins at exactly the same speed. As the disc spins, it rotates within the magnetic field produced by the coil. The individual teeth on the disc create an interference pattern, picked up by the receiver.
The faster the interference pattern comes through, the faster the car is moving. The ECU then translates these readings into useful data, showing the rpm level on the meter on your dashboard, if your car has one.
Most modern engines have a manufacturer-set top speed that they will rotate at; this is a maximum rpm, preventing the engine from overworking itself and breaking. These limits are often imposed electronically, and this sensor is a crucial part of that system.
If the Engine Speed Sensor is Faulty, What Might Happen?
If you have a problem, the incorrect readings will be sent to the rev meter. If you have had your car for a long time, you are unlikely to use the rev meter much. However, if you have a new car or have recently bought a second-hand vehicle, the rev meter can be handy for knowing when to change gear. This is especially in a manual transmission while you get used to the feel of the car. If the sensor is noticeably damaged, you’ll notice that the reading on the dashboard seems too high or too low.
If this has happened, you’ll also notice the following symptoms:
- Cruise control won’t be working correctly – Because the sensor isn’t working properly, the ECU will automatically prevent the cruise control from working. You may not use your cruise control very often and might not notice this – we would recommend taking your car out and turning on the cruise control if you think this sensor could be malfunctioning. If the car seems incapable of maintaining cruise control, it could be due to the Engine Speed Sensor.
- The check engine light will be on – With modern cars, there are more and more internal checks that the cars will do. If the Engine Speed Sensor fails, internal checks will usually be able to tell this. Although you won’t know the exact cause just from looking at your dashboard, taking your car to a mechanic with a code reader should solve the problem for you.
- Strange shifting patterns – Again, because the car thinks that the engine is working at a different speed to what it actually is, you may notice unusual shifting patterns. These will be either the car shifting earlier or later than you would typically expect.
The Best Way to Diagnose These Problems
There are so many sensors and electrical circuits in modern cars that it can be impossible to diagnose the problem yourself. You’ll probably need to take it to a garage to get it fixed anyway, so there’s no harm in asking them to diagnose the problem as well. The mechanic will attach an OBD (on-board diagnostics) code reader to your car. This code reader will “read” information from the ECU, including a specific error code. If there’s a fault with the Engine Speed Sensor, this will let you know.
To get your Engine Speed Sensor changed at the garage, expect to pay approximately $10 – $60 for the sensor itself, plus an extra $50 – $70 for labor. As well as providing you with different quotes for sensors of varying ranges of quality, different garages also charge different labor rates, so don’t expect every garage to quote you exactly the same amount. Shop around a bit, but don’t trade out the quality for price – you will end up needing to change it again sooner rather than later.
It’s certainly possible to change the Engine Speed Sensor by yourself, but since it’s such an integral part of the car, we would only recommend doing this if you’re certain you know what you are doing. Changing this sensor can be difficult and will leave you cursing the air because of your bruised knuckles.
You should always make sure that your Engine Speed Sensor is working. It will keep everything ticking over nicely and leave you with less to worry about.
Hopefully, this article will have given you a little more information! We hope you don’t run into this problem but, if you do, be sure to take your car to a qualified mechanic who can help you out.