What does the car's speedometer measure, how it works, and signs of malfunctions

Every motorist must have a day and wonder what exactly does the speedometer in a car measure? And what is its mechanism of action? Some may also have problems with the speedometer and want to know the most prominent general reasons that may lead to a breakdown of the speedometer and the signs of a failure in the speedometer. Of all the tools you can find on a modern car dashboard, only one is required by law, and that's the built-in speedometer and odometer (also called an odometer). What does the car's speedometer measure, the way the car's speedometer works, the reasons for the speedometer malfunction, and the signs that the speedometer has failed.

The direct answer to the question of what the car’s speedometer measures is the instantaneous speed, and in order to measure it, it takes several other measurements and depends on some data and sensing some other data, as will be discussed in detail in the paragraph “How the speedometer works.” The speedometer also measures the distance traveled during the trip and the total distance traveled since the first day of using the car; They are measured by an instrument built into the speedometer called an odometer.

How the speedometer works :

After identifying the answer to what the speedometer measures in a car, in the following lines we will introduce you to how the speedometer works: Mechanical speedometers measure the car's instantaneous speed based on simple data, namely knowing the size of the wheels and tires and measuring the rotation rate of the wheel. The rotating wheels are intelligently connected to the speedometer indicator using electromagnetism; The shaft that turns the wheels of the car (the wheel hub) is connected to the speedometer via a long, flexible cable made of twisted wire. The cable is like a small shaft: if one end of the cable rotates, the other also rotates, even though the cable is long and curved. The cable from the top end of the magnet feeds to the back of the speedometer inside a case, and when the cable rotates, the magnet case inside the speedometer rotates at the same speed. The magnet rotates inside a hollow metal cup, known as a speed cup, which is also free to rotate, although restricted by a thin coil of wire known as a capillary spring. However, the magnet and the speed cup are not connected to each other. The speed cup is connected to the indicator, which moves up and down the speedometer dial to give us a reading of the instantaneous speed of the car.  

electronic speedometers :

 Electronic speedometers are now more and more popular, although mechanical ones are generally reliable. The most common type of electronic speedometer has a magnet attached to the gearbox output shaft and an electronic unit placed near it to act as a charge vector; Each time the rotating magnet passes the pickup, the unit sends a pulse of electric current through the cable to the speedometer. An electronic box inside the speedometer measures the pulse and calculates the vehicle's speed. 

What makes the speedometer measurement inaccurate :

After identifying the answer to what the speedometer measures in a car, which is the instantaneous speed as we explained, it should be noted that the speedometer measurement may be inaccurate, and here is the most prominent reason. 

Both the speedometer and odometer depend in calculating the speed and distance traveled on the size of the wheels and tires, to calculate the distance traveled by calculating the rotation of the wheels, so the distance traveled is the number of times the wheels rotate multiplied by the circumference of the tire, which is the standard tire diameter multiplied by pi (3.1416) . If non-standard, worn or air-deficient tires are used, the accuracy of the meter reading will be reduced

Causes of speedometer malfunction:

 After answering the topic question: What does the speedometer measure in a car? Talking about the main reasons for the failure of the speedometer in the car, they are: Malfunction of the wheel rotation sensors Car engine control unit problems that cause speedometers to get wrong data Damage to the cable between the wheel hub and the speedometer or valves, and this may be from internal combustion in the wiring  

Signs of a broken car speedometer :

After we got to know the answer to the topic question: What does the speedometer measure in the car, and then we mentioned the most important reasons for the speedometer malfunction in the car, we will introduce you in the following lines to the common signs of malfunctioning speedometers: 

The speedometer has stopped working completely, and you find that the speed indicator has stopped permanently, or has become intermittently working, or it was clear that it is not working accurately, such as changing the reading quickly with no change in the speed of the car. A malfunction in the cruise control: The sensor that the speedometer system depends on depends on the cruise control system found in most modern cars. Speed ​​on it in order to control the accelerator pedal to keep the car at the set speed. 

Car slowness:

If you notice that pressing the accelerator pedal does not produce the usual force in cars that rely on electronic fuel injection technology, the cause may be related to a malfunction of the speedometer. 

Check Engine Light:

 In some cases, the check engine light comes on when there is a malfunction in the speedometer sensors. Either way, turning on the check engine light requires getting maintenance and promptly fixing the problem. 

Abnormal movement of the speedometer indicator:

 It is normal for the movement of the speedometer pointer to be very smooth to be a measure of the car’s instantaneous speed in various driving situations, including acceleration and deceleration. The speedometer is associated with getting wrong data from the sensors, so you should go to a service center and fix the problem