Regardless of how exactly the speedometer shows speed, it is considered one of the most important devices in a modern car. We are forced to look at his testimony, otherwise we will not be able to avoid punishment for violating the speed limits in force in the country.
What is a speedometer/odometer combination?
The combined instrument indicates the driven speed in the car, measures the mileage traveled, shows the mileage of one trip and the instantaneous speed.
Attention! The speedometer scale helps the driver determine when to replace engine fluid and filters and calculate fuel consumption.
The speedometer is sometimes equipped with an odometer - a mechanism that measures the number of revolutions of the car's wheel. This way, the mileage traveled by the car is determined. It is possible to calculate daily and total mileage.
The odometer consists of:
- car revolution counter;
- an indicator showing the distance traveled in km or miles;
- speed recording device.
Odometers are classified into the following types.
- The mechanical device is considered the progenitor of modern devices. It was invented back in Ancient Greece.
Twisting such an odometer is as easy as shelling pears; all you have to do is act on the twisting mechanism. The mechanical odometer counter reacts to revolutions and converts them into kilometers. However, the disadvantage of such a device is that the data spontaneously resets when a certain value is reached. - The combined odometer is an improved model that makes it possible to correct data using a CAN rotary.
- A digital device operating on the basis of a microcontroller. Everything in such an odometer occurs digitally, and the readings of the device can only be influenced with the help of highly professional equipment. Electronic odometers are part of the car's on-board computer system.
The principle of operation of the speedometer is clearly visible in the example of a mechanical device. The speed change is carried out due to a mechanical connection between the gear shaft and the pointer. Both elements are connected by a cable of sufficient length, since the shaft is located far from the transmission. Its speed is determined by the finite amplitude of rotation of the wheels.
A special gear in the main gear rotates together with the output pulley and is also directly connected to a cable enclosed in a special protective casing.
Another required element is a disk-shaped magnet placed next to the steel drum. The latter is fixed to the needle, and the obtained indicators are displayed on a scale.
Even the electronic odometer has inaccuracies. They cannot be excluded, therefore it is customary to take into account certain standards that allow a limit to this value. For example, on a mechanical device the error should not exceed 5% -15%.
Device errors are explained by the presence of various gaps, weakness of the cable, poor grip and weak springs. A mechanical odometer produces more errors, a digital one produces much less, because it is possible to read the readings of a microcontroller and sensor.
There may also be an error on the speedometer, which calculates the speed of the car. The device is simply unable to display perfectly accurate information, since the speed depends on several components: rotation of the wheel, its diameter, etc.
It will be interesting to monitor the errors of the device at different speed modes.
- 60 km/h - there are almost no errors.
- 110 km/h - the error is 5-10 km/h.
- 200 km/h - the average value reaches 10%.
The error also varies according to the following points.
- On cars with front-wheel drive, the error appears at almost every turn. The reason is that the speedometer is integrated with one wheel. Because of this, turning to the left decreases the readings, turning to the right increases them.
- The error is affected by the non-standard wheel size. A difference of 1 cm increases the error to 2.5%.
- The diameter of the tire is important. At the slightest discrepancy with the standard, the speedometer readings are underestimated or overestimated.
- Tire pressure and tread wear can affect the error. For example, if the tire is poorly inflated, this leads to an underestimation of the maximum speed.
The most accurate readings are given, as mentioned, only by a digital device or a device connected to a GPS navigator. The benefits of satellite positioning cannot be underestimated. Modern systems demonstrate the exact speed of the vehicle without any errors.
The standard speedometer is marked with a scale of 10 km/h, and its needle twitches on potholes. He can only overestimate the readings, but not underestimate. Otherwise, the road situation will be falsely assessed and an emergency situation will arise. For example, if 100 km/h is displayed instead of the real 120 km/h.
A few words about errors associated with tire sizes. This is where the design of the speedometer itself comes into play. It consists of two devices combined in a single housing. One device measures speed, the other shows the vehicle's mileage. So they are called: high-speed and counting nodes.
Now specifically: if the car is shod with tires that are quite worn, the speedometer will overestimate the readings, since the gradation system comes into force every 10 km/h and the law of rounding numbers used in odometers.
Differences: speedometer and odometer
The odometer is mounted directly into the speedometer itself. For this reason, many people think that the device is a single device. Actually this is not the case:
- the speedometer only shows the speed of the vehicle;
- odometer - indicates the distance traveled in km.
The functionality of both devices is not interconnected, and the combination of both scales only affects the convenience of the driver.
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Every third report from the Autocode service shows that the car’s mileage is incorrect. On average, each car travels about 20 thousand km per year. However, on sale you can find many 5-7 year old vehicles with mileage of 50-60 thousand km, or even less. Owners of such cars may claim that they only used the car “on major holidays.” But, most likely, the actual mileage is much higher than that indicated on the dashboard. Let's figure out what methods fraudsters use and how to determine the twisted mileage.
Why do they twist the mileage?
Most often, the odometer readings are changed in order to sell the car at a higher price. However, there are a number of other reasons why sellers resort to this procedure. Twisting of readings may be caused by the need to:
- avoid expensive maintenance (the on-board computer of some foreign cars contains information about the time of maintenance; if this schedule is violated, it begins to issue alarm messages);
- hide the fact of replacing the dashboard (after an accident or for other reasons);
- keep silent about malfunctions of components that may affect the correct operation of the speedometer (for example, generator, battery, etc.).
You may be faced with the fact that the mileage of used cars imported into Russia from those countries where the amount of transport tax is calculated depending on the kilometers traveled by the car over a certain period of time is increased.
For example, such a system has been in operation for several years in the Netherlands, where a car’s mileage is tracked using GPS. In some US states, car owners have to pay $0.012 per mile.
By the way, under American law, mileage abuse is a criminal offense. Serious liability for such actions is provided for in Germany and France (up to 1 year and up to 2 years of imprisonment, respectively). Russian legislation does not provide for punishment for mileage inaccuracy.
Ways to twist mileage
Fraudsters have several techniques in their arsenal to deceive gullible customers. The choice of one method or another primarily depends on the type of device installed on the machine, which is responsible for calculating the distance traveled.
Here it is necessary to clarify and talk about the fact that many inexperienced car owners mistakenly associate the increase in mileage with adjusting the speedometer readings. In fact, it shows the speed of movement, and the number of kilometers traveled by the vehicle is recorded by another device - odometer.
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The device works in close connection with the speedometer. And the panels that display the readings of these two devices are usually located next to each other. Apparently this is where some confusion in concepts arose. In order not to confuse the reader even more, we agree that the use of both definitions is acceptable.
A car can be equipped with one of three types of odometers:
- mechanical;
- electromechanical;
- electronic.
Mechanical and electromechanical devices were used in the automotive industry until the end of the last century. They are distinguished by a rather primitive device: the speed of the gearbox gearbox is transmitted through a special cable to a meter, the readings of which are displayed on the dashboard. It is easiest to check the mileage of such a device.
Method number 1. The odometer is disassembled, and the necessary readings are set on the meter manually.
Method number 2. To implement it, you will need to disassemble the dashboard and attach any power tool with high rotation speed (screwdriver, drill, etc.) to the speedometer cable using a special attachment. After this, the readings are twisted to the desired value. Of course, this can be done manually, but using a power tool speeds up the process many times over.
For an electromechanical odometer, twisting is carried out in a similar way. The only difference is that if, when taking readings from a mechanical device, the on-board power of the car is turned off (the terminals from the battery are removed), then when carrying out manipulations with an electromechanical device, the power cannot be turned off (otherwise the meter wheels will not rotate). Therefore, there is a high probability of a short circuit occurring.
The cost of the work is quite affordable and ranges from 1 to 1.5 thousand rubles. It’s quite easy to find advertisements in newspapers or on the Internet for companies willing to provide such a service. They are usually hidden under signs like this: “Speedometer adjustment and repair.”
Quite a few home-grown “Kulibins” in their own garages make a living by turning mileage. Usually people find out about them through word of mouth.
Rolling up the electronic odometer
The operation of devices of this type is based on reading the readings of special sensors (they can be optical or magnetic), which are installed on the gearbox shaft or directly on the vehicle wheel. The readings go into the on-board computer, which records them and transmits them to the electronic display.
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On expensive car models (Toyota, Audi, etc.), mileage data can be stored in several memory blocks at once. According to experts, it is most difficult to change the mileage traveled on a BMW (the car can have up to 10 backup storage points). However, experts unanimously claim that if you have the appropriate equipment, you can check the mileage of absolutely any vehicle.
Several tricks are used to manipulate electronic odometers.
Method number 1. Designed for fraud with budget cars. To implement it, it is enough to remove the dashboard and connect the car’s on-board computer to a laptop on which the appropriate software is installed, or to a special device - a programmer. After this, the actual readings change.
Method number 2. Used for fraud with expensive cars that have several backup data storage units. In its principle it is almost identical to the first. However, it is very important for the fraudster to detect all information storages, otherwise during further operation the car computer can restore data from the backup storage, then the real mileage will again be displayed on the display.
The cost of the service depends on the complexity of the work and can vary from 2.5 to 10-12 thousand rubles.
How to check if the speedometer on a car is twisted
In order not to overpay for a supposedly “almost new car,” you need to remember how you can find out about the fact of fraud.
Unfortunately, there is currently no technical means of checking whether the mileage has been adjusted or not on a vehicle with a mechanical or electromechanical odometer.
Here you will have to be guided by the data of the external examination. The fact that the speedometer is twisted can be determined by the presence of traces of removing the instrument panel, the degree of wear of tires, brake discs, etc.
How to find out if the mileage on a car with an electronic odometer is wrong
To establish the fact of fraud, you will need to conduct computer diagnostics. If you have the appropriate software, equipment and knowledge, you can check the car for twisted mileage yourself. But it is better to contact a trustworthy service center.
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The ideas of many car enthusiasts about the wonders of computer diagnostics are too exaggerated. Those who think that there is a special item in the memory of the on-board computer, by looking into which you can check the real mileage, are mistaken. Most often, you can find out about the fact of interference in the electronic filling of a vehicle only by indirect signs.
Usually this is a discrepancy in data, for example, about the time of an event recorded by the on-board computer. For example, if during a check the car’s odometer shows 75 thousand km, and the memory contains information about an error recorded after 150 thousand km. Or the owner swears that his “iron horse” has run no more than 50 thousand km, but when dividing the kilometers traveled by the number of engine hours, the average speed of movement is 4-5 km/h.
The more such oddities revealed by checking the car’s speedometer, the more reason the buyer has to wonder whether he needs such a “dark horse”.
How to find out real mileage online
You can check whether the mileage is twisted on the website. To do this, just enter state in the search bar. vehicle number. After this, within a few minutes you will receive a full report about the desired vehicle.
In addition to data on actual mileage, using the service you can obtain information about the number of accidents in which the vehicle was involved, former owners, the presence of fines, check for restrictions and find out a lot of other information from the car’s history.
One of the main factors that you need to pay special attention to when purchasing a new vehicle is the mileage traveled by the car. But you shouldn’t blindly believe the odometer readings. Not entirely conscientious car owners, trying to sell their “iron horse” at a higher price, deliberately underestimate the real odometer readings through fraudulent means. However, determining the fact of twisting is a difficult and sometimes impossible procedure. When assessing the actual mileage of a car, it is advisable to start from indirect signs.
Naturally, if the odometer readings have been tampered with, then this can be determined. And everyone who wants to buy a used car should know how to find out if the mileage is incorrect. To this end, you need to build on a whole range of both direct and indirect evidence. By direct factors, you can accurately determine that changes have been made to the odometer data. In its turn, by indirect evidence You can find various discrepancies between the technical parameters of the car and the actual mileage readings.
In most cases, mileage readings are changed in order to inflate the actual value of the car. Therefore, the buyer is at great risk of purchasing a vehicle in technical condition, the main components and assemblies of which are badly worn out.
In some countries, mileage reduction is done in order to reduce government taxes when selling a car. This is because tax amount directly depends on the mileage traveled by the car over a certain time period.
Cases of an increase in the actual mileage of a car have also been recorded. The purpose of this fraud is to convince the buyer that he will not have to carry out expensive scheduled maintenance when the vehicle reaches 90-100 thousand km. The buyer purchases the car with the confidence that all worn parts have been replaced and the car is in perfect condition. In reality, the new car owner will face constant repairs.
Which brands of cars have their odometers twisted more often?
Most often, twisted mileage can be found in domestic and Japanese cars, as well as some models of cars produced in Europe. German-made cars are better protected from external interference. They duplicate any changes using different special devices. The most resistant to fraudsters' interference are considered to be BMW cars, in which the mileage readings are duplicated by a chip in the ignition keys.
The mileage of many Japanese cars can be found in the documents accompanying them. If you purchase a car at an auction, an auction sheet is attached to it, which contains the exact information of the odometer readings. If we look at European and domestic cars, whether the mileage in them has been increased or not can only be determined by indirect evidence and there are no other methods.
How to determine whether a mechanical odometer is twisted?
Any vehicle has the ability to change actual mileage readings. If the vehicle is equipped with a mechanical odometer, the mileage change is performed two simple methods.
If the buyer has doubts that the mileage of the mechanical odometer has been twisted manually, then an external inspection of the device must be carried out. The numbers on the meter should rotate smoothly without jumps while the machine is moving. Also, by carefully examining the dial, you can see a dark space that separates adjacent values. If it is discovered that it has changed its color, it can be argued that someone tampered with the odometer.
In case of mileage changes using an electric drill It is almost impossible to detect interference with the operation of the device. In such a situation, one must proceed from the external state of the car’s components, which must visually correspond to the indications of the distance traveled by the car.
How to find out whether the electronic odometer has been tampered with?
In electronic vehicle mileage meters, all information is stored in memory. Therefore, in order to change the real data of the device, special computer equipment is used. In some cases, they even use replacement of microcircuits and individual electronic boards.
To find out the consistency of the odometer readings, it is best to contact a professional car service center, where they will carry out the appropriate diagnostic measures. Although, if you wish, you can try to find out whether the mileage of the vehicle is twisted on your own.
If carried out re-soldering of the microcircuit, then it was preceded by disassembling the dashboard. Therefore, you can inspect all attachment points for defects or scratches that could have been caused during disassembly. Also, when you get to the odometer board, you can see that it was heated with a soldering iron, since the layer of factory varnish will be damaged. Plus, the readings of the electronic device are additionally recorded by the on-board computer system.
Today, experienced car owners use several ways of indirect determination twisting mileage:
- visual inspection of interior parts;
- scrupulous study of technical documentation for the car;
- measuring the tire tread height;
- checking the condition and quality of operation of the main vehicle systems.
When inspecting the interior of a car, you need to pay attention to the condition of the seats, steering wheel, car mats and rubber pads on the gas pedals. If severe wear is detected on any components of the car's interior, we can say with confidence that it has a solid mileage.
You can find out about changes in odometer data from the seller's stories o undergoing scheduled maintenance, which must be marked accordingly in the service documentation for the car. If any discrepancies are detected, we can confidently say that they are trying to deceive the buyer. In such a situation, you can contact representatives of the service center where the car was serviced and find out the actual mileage using the VIN code.
You can ask the seller when the last time the tires were replaced. If the car has original slopes, then you can find out the actual mileage based on the tread height. If the car has driven no more than 30–50 thousand km, then the tread depth will be within the permissible limits established by the manufacturer.
There is another factor that indicates interference with the odometer - severe wear of the brake discs. Although such consequences can be observed if the motorist prefers an aggressive driving style. Also, in case of high mileage, you can find many small chips and traces of abrasions from the windshield wipers on the windshield.
Condition of components The car body will not always help determine how many kilometers the car has traveled. If a car owner takes good care of his car, then even after 200 thousand kilometers, the appearance of the vehicle practically does not change. Therefore, only service center specialists will be able to give an accurate answer whether the mileage has been adjusted or not.
But even after familiarizing yourself with how to determine the real odometer readings when purchasing a vehicle that is not new, the main attention should be paid to its technical condition. It does not in all cases depend on the age of the car. After all, there are still many motorists who really care about their car, maintaining it in working condition. Even after 300 thousand kilometers, such a car will look no worse than a vehicle that recently left the showroom.
Over time, the car’s speedometer begins to incorrectly show the true speed of movement, and at the same time the trip meter also lies. The same picture will be observed in any car if “non-original” wheels are installed on it, namely, with a higher or lower profile.
The latter occurs due to the fact that the rolling radius of the wheel changes. At the same time, correct readings of the speedometer and trip meter are very important for the motorist, as they allow optimal planning and avoiding misunderstandings with the traffic police regarding the issue of speeding. So checking your speedometer is not very harmful.
This exact job can be done without removing the speedometer from the car, without the help of any special additional instruments and devices. To do this, place reliable stops under the non-driving wheels of the car, and the drive wheels must be suspended. Next, start the engine and set the speedometer to 40 km/h. Then use the second hand of your watch to measure the time between any two trip meter readings.
The actual speed (V) of the car will be equal to: V=(S2 - S1)/t (km/h), where S1 and S2 are the meter readings at the beginning and end of the measurement (km); t - time between readings S1 and S2 of the counter (hours). Repeat the same check at a speed of 80 km/h. By comparing the speed calculated and set using the speedometer, you can determine the error of the speedometer.
Checking the correct operation of the trip meter and speedometer can be made even easier if you are going on a long trip on a good, dry highway. Notice a kilometer post on the highway and a car trip meter reading. Drive along the kilometer posts for exactly 100 km. and note the meter reading on the vehicle. The difference in the readings constitutes the error of the meter and, indirectly, the speedometer.
For example, if you drove 110 km according to the meter, then it is clear how much it is wrong. The speedometer - the speed indicator - also lies. If you are driving at a speed of 100 km/h according to the speedometer, then in reality (for the traffic police inspector) your speed is 110 km/h. It is useless to search for the truth later. This is precisely where the author of these lines got burned once, when, after installing high-profile Moskvich M-145 tires on a VAZ-2102 car, he did not take into account the inevitable distortion of the speedometer readings.
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The speedometer, as the name suggests, shows the speed of the vehicle. Following the speed limit is important not only to avoid fines, but also to make safe turns and other maneuvers. The higher the speed, the larger the safe turning radius should be. If the radius is less than necessary, there is a high probability of the car skidding and overturning the car. Therefore, the serviceability of the speedometer is as important as the high-quality operation of the steering or braking system.
How does a speedometer work?
There are two main modifications of speedometers:
- mechanical;
- electronic.
The principle of operation of a mechanical speedometer is to transform the shaft rotation speed into energy, which moves the needle. The speedometer drive is located in a manual or automatic gearbox and is connected to the indicator using a flexible cable protected by a metal casing. The tips of both sides of the cable are made in the form of a tetrahedron, due to which they effectively transmit rotation from the drive to the indicator. A mechanical speedometer is always connected to the odometer (vehicle mileage indicator) and forms a single unit with it.
The operating principle of an electronic speedometer consists of a sensor that produces pulses of a certain frequency and duration (depending on the speed of the car). The sensor is connected either to a separate electronic speedometer or to the on-board computer. Both the computer and the speedometer perform the same function - they count the number of pulses per unit of time and convert the value into understandable kilometers or miles per hour.
Speedometer malfunctions
The most common malfunctions are:
- cable break or damage;
- the cable tip jumping off the driven gear;
- malfunction of the mechanical or electronic indicator;
- pulse sensor malfunction;
- poor contact or broken wire that connects the sensor and the indicator or computer.
Video - How to fix a speedometer
Diagnostics and repair of a mechanical speedometer
- For diagnosis you will need:
- 12 Volt motor;
- flat and Phillips screwdrivers;
- flashlight; jacks and stands;
- instructions for repairing or servicing your car.
To check the speedometer, raise the front passenger side of the vehicle using a jack. For information on how to do this safely, read the article (Replacing and restoring shock absorbers). Remove the front panel (dashboard) to access the instrument cluster. On some car models you can do without this operation, so carefully read the repair and operating instructions for your car. Remove the instrument cluster and unscrew the cable fixing nut from the indicator, start the engine and engage 4th gear. Check if the cable is spinning in the protective casing? If yes, turn off the engine, insert and tighten the cable end, then start the engine again, engage 4th gear and look at the indicator readings. If the arrow does not change position, the indicator is faulty and must be replaced.
If the cable does not turn when the engine is running and the gear is engaged, it is necessary to turn off the engine and remove the cable from the drive located on the driver's side of the gearbox. Pull the cable out of the engine compartment and inspect the ends to see if the shape (square) is damaged. Twist the tip on one side of the cable and observe the tip on the other side. If both tips rotate synchronously, without effort, and the edges of the tips are not licked, then the problem is a worn drive gear, so it needs to be replaced. This operation is described in the vehicle repair and operating instructions.
Diagnostics and repair of electronic speedometer
For diagnosis and repair you will need:
- flat and Phillips screwdrivers;
- tester;
- a set of keys;
- scanner for an injection engine (you can use a regular oscilloscope instead).
Run self-diagnosis of the on-board computer (BC). On most fuel-injected cars manufactured after 2000, the BC supports this function. If the BC gives an error, you need to decipher it using a special table, which is located in the instructions for servicing and repairing your car. But, the diagnostic results will show whether the entire speedometer system is working or not. To fix the problem, you will have to look for the damage yourself. To do this, lift the car as described above. Connect the oscilloscope to the middle contact of the speed sensor (installed in place of the speedometer drive) and the positive contact of the battery. Start the engine and engage 1st gear.
A working sensor will produce a pulse signal with a voltage of at least 9 Volts with a frequency of 4 - 6 Hertz. If the sensor is working properly, you need to turn off the gear and use a tester to check the wire that connects the sensor to the electronic control unit (ECU) controller. Or use an oscilloscope to check the sensor signals at the ECU input. If there are signals, you need to check the terminals and wire that connects the ECU and the instrument cluster (speedometer indicator). If you have a special scanner, then it is advisable to check the speedometer indicator, this will allow you to more accurately determine the cause of the malfunction.
Most often, the speedometer stops working due to water and dirt getting into the terminals, as well as due to a break or break in the signal wires. Therefore, in most cases it is enough to dry and clean the contacts. If the test results indicate that the speed sensor is faulty, it will need to be replaced. This procedure, as well as replacing a damaged indicator, is described in detail in the operating and repair instructions for your car.
