What is an odometer and what is it for
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What is an odometer and what is it for


How long will the ride take? This question often arises from the driver when he is driving in unfamiliar terrain. In this case, it is very difficult to determine the exact driving time - it is not known what the quality of the road is, and whether there are traffic jams on it. But the remaining distance can be determined.

For this purpose, an odometer is installed in the vehicle. What is this device? How does he account for the distance traveled and what is the risk of its breakdown? Let's consider these and other questions in order.

What is an odometer?

An odometer is a counter that measures the distance the vehicle has traveled. It is installed in the dashboard in the section for the speedometer (a window in its scale for better perception). The instrument on the panel looks like a window with numbers.

What is an odometer and what is it for

In the classic version, this device has two lines with numbers. One indicates the actual mileage of the car since the installation of the meter. The second line is called the daily mileage counter. It shows the kilometers traveled by the car since the dial was set to 0 (there is a corresponding button for this).

What is an odometer for?

In addition to the fact that the odometer helps the driver to record the distance traveled, the device also provides practical assistance when buying a car on the secondary market. The mileage shown on the main odometer line will tell you whether it's worth taking a relatively new car at a low price. This combination immediately raises doubts.

Functional properties of the device

Here are a couple more useful counter functions:

  • The driver can use the mileage to determine when the vehicle needs scheduled maintenance. At the same time, it is important to fix the indicators and write them down somewhere so as not to forget;
  • In cars, the control unit of which does not indicate the total and current fuel consumption, the odometer will help determine the "gluttony" of the car;
  • If the fuel level sensor breaks down, after a full refueling, the daily counter is set to zero. After the gasoline in the tank (or gas in the cylinder) runs out, the actual consumption is calculated;
  • Allows you to determine how much is still left to drive to the destination, if you know the exact distance from point "A" to point "B".
What is an odometer and what is it for

Resetting the counter is possible only for the daily mileage, and the main indicator is not reset to zero. This function is useful when there are disputes between the employee and the employer regarding the use of a company or personal vehicle.

The manufacturer did not specifically provide for a general reset of the mileage, so that the driver did not do it accidentally or in order to hide important data from persons who have the right to have this information.

How the odometer works

The odometer is designed in such a way that each kilometer traveled by the car corresponds to a certain number of wheel revolutions. Moreover, this parameter does not change. The only exception is when a motorist installs non-standard wheels on his car. In this case, the odometer will also show a specific mileage, but the device will have a large error.

What is an odometer and what is it for

This must be taken into account, since the panel will indicate the wrong mileage - either more or less. It depends on whether maintenance is carried out on time.

The device includes the following elements:

  • Wheel sensor - Installed near one of the front wheels. There are modifications with a sensor in the wheel itself, and there are also models of odometers with a sensor that is installed in the gearbox. In each individual case, the measurement will be carried out in accordance with which part of the car this element is installed;
  • Odometer drive - reads the speed indicators and, depending on the type of device, transfers this indicator either to the ECU, or directly to the dial through the gears. In many electronic odometers, such mechanisms may not be used, and the signal from the sensor via wires is immediately sent to the control unit;
  • Screen - in electronic modifications, it displays the indicator calculated by the control unit (the algorithm is set by the manufacturer or by the software after firmware) based on the revolutions of the drive wheel.

Reading accuracy

Any odometer, even if standard wheels are used, has an error. This is allowed because meters do not play as much of a role for a car's mileage as kilometers.

And the maintenance of the car is generally carried out through a certain number of thousands of kilometers. For this reason, the error of mechanisms (and even an electronic analogue) can range from two to ten percent. Also, the device records the number of kilometers, not centimeters or meters.

What is an odometer and what is it for

In addition to the factory error in a car with high mileage, the device can give even less accurate readings. This is due to wear of parts or failure of the sensor.

Odometer correction

Since many factors affect the accuracy of odometer readings, this device cannot be called perfectly accurate. But even with a small percentage of error, if the car drives long distances every day (for example, the owner is a taxi driver), then the odometer will still have an impressive figure.

It will not be possible to profitably sell such a car on the secondary market, even if the car was bought in the showroom relatively recently. In order for the owner of such a vehicle to be able to sell it at a higher price, some go to the trick of adjusting the mileage counter. For more information on how to determine that this parameter has been changed, read in a separate review. A here see recent research on which car is more likely to have a twisted mileage.

Unfortunately, there are so many sellers involved in rolling mileage that pre-sale odometer adjustments have become a tradition. If we talk about mechanical models of meters, then traces on the case or clamps will indicate a change in the mileage figure. With regard to electronic odometers, it is impossible to visually determine such an adjustment. For diagnostics, you will need special equipment that looks for a discrepancy between error codes and odometer readings (the control unit records the mileage at which this or that error appeared).

Types of devices

There are three main elements in the odometer device:

  • The panel on which the traveled mileage is displayed;
  • A mechanism that reads the revolutions of the drive connected to the wheels;
  • A controller that converts the number of revolutions of the drive shaft into an indicator of kilometers traveled.

The machine can be fitted with a mechanical, electromechanical or electronic odometer. Let's consider what is the difference between them.

Mechanical odometer

This modification considers the distance traveled mechanically. The design of such a meter has a drive cable placed in a steel casing with a braid that protects against metal contact with moist air, which would quickly rust the part.

This modification of odometers is connected to the gearbox (output shaft), and on the other hand, to a mechanical counter. On average, one kilometer corresponds to 1000 revolutions of the drive cable. Rotating, the first gear (on the end of each of them there are numbers) after each full circle clings with a pin to another gear, which rotates one division.

What is an odometer and what is it for

Each gear engages the next only after 10 revolutions have passed. Newer mechanical odometers have a set of gears that have a gear ratio of approximately 1690 to 1.

Electromechanical and electronic odometers

Electromechanical and electronic odometers read the mileage in a similar way, only the indicator is displayed on an electronic display. Most models use a magnet and a gyro. When the magnetic marker passes the sensor, the electronics fixes the revolution and the information on the display is updated.

Most of the mechanisms for such odometers are also connected to the gearbox. In some models, the electronic odometer is synchronized with the control unit, which records the revolutions of the driving wheels (for example, in the ABS system).

What is an odometer and what is it for

There are optical electronic odometers. Instead of a magnetic gyro, they use an optical sensor and a slotted wheel. The number of kilometers traveled is determined by algorithms embedded in the control unit, from which a digital signal is sent to the odometer screen.

Odometer and Speedometer: What's the Difference?

Since the mechanism for the speedometer and odometer is the same, and their indicators are displayed in one cell on the panel, many motorists believe that this is the same device. In fact, these are different devices that show different results. A speedometer is needed to measure vehicle speed. While the machine is at rest, the instrument needle does not move either.

What is an odometer and what is it for

As for the odometer, when the wheels rotate, it indicates not the speed of this action, but the distance that the car has covered during the entire operation period and at a certain interval.

Odometer breakdown

Malfunctions of this device are rare, since it has a minimum of mechanisms that experience significant mechanical or thermal stress. Mechanical devices break down more often due to design features. In electronic and mixed versions, the breakdown is mainly associated with the failure of the sensor that reads the rotation of the wheel.

When buying a car on the secondary market, you must first determine if the mileage was twisted by the previous owner. The options for detecting such frauds are described in a separate review.

In the event of a failure of the old model, repairs must be carried out as carefully and carefully as possible, since even minor errors (for example, the counter fixation is incorrectly fixed) can greatly affect the accuracy of the device.

What is an odometer and what is it for

It is much easier with an electronic sensor - if it breaks down, then a new one is simply connected to the appropriate connectors of the system. If there is a failure in the control unit, it will not be possible to solve the problem on its own, since complex professional equipment will be required to eliminate the error.

Causes of breakdown and repair

Breakdowns and incorrect operation of the odometer depend on the type of meter. The most reliable odometer is electronic, inextricably linked with the on-board computer. Here are common breakdowns of different types of odometers:

  1. Mechanical meters fail due to wear of gears and other parts of the mechanism. In the event of an accident, the odometer cable may break or the mechanism itself may crumble, due to which the meter either does not work correctly or stops working altogether.
  2. Electromechanical odometers are more likely to fail if contact is lost between the meter and the wheel sensor. Less often, the microchip of the device breaks down.
  3. Electronic odometers generally stop working correctly due to interference with the software, for example, when trying to twist the mileage.

Why rewind the mileage readings in the car

There is only one reason for twisting the car's mileage. This procedure allows you to hide the real technical condition of the car. For example, the prospective buyer is misled about the life of the engine, transmission and various systems that need to be replaced with high mileage.

What is an odometer and what is it for

Having twisted the mileage, the seller can either claim that the engine is still far from one million kilometers (often such motors need a major overhaul). Or vice versa, he can convince that the car has passed only an insignificant mileage after the overhaul of the power unit.

In each case, the purpose of such a deception is to sell a pretty beat-up car at a higher price. Low mileage is the main reason why inexperienced car owners agree to such a high price for a used car.

Twist - odometer correction

This procedure is used by dishonest car owners planning to sell their car. The reason for this is the reluctance to invest in a vehicle, but a great desire to bail out more money from the sale.

Every car after a certain mileage needs regular maintenance, not just because of the manufacturer's desire. Mechanisms and systems after a certain time need to be repaired, and in some cases even to be replaced.

When a smart buyer chooses a used car, he pays attention to the condition of the car, including looking at the odometer. If the mileage is decent, then it specifies when the maintenance was performed. To mislead the client, some twist the run backwards to give the impression that this procedure is still very far away. Others, on the contrary, wind up the run, and so the buyer has the idea that MOT has already been done a long time ago.

What is an odometer and what is it for

It is more likely to buy a car with a twisted range - equipped with a mechanical odometer. It is much more difficult to do this with an electronic counterpart. To do this, you need to intervene in the software of the control unit, therefore, when buying such a car, it is imperative to carry out deep computer diagnostics.

During diagnostics, a professional will immediately see a discrepancy in the computer data. For example, the on-board system in memory may have a message about an error of any sensor with a mileage of 105, and during diagnostics the odometer shows 000, and the car owner convinces that no one has done anything with the electronics. It is better to refuse such a "tempting offer".

For more information on how to recognize the real condition of a used car, see the video:

How to find out the real mileage on AUTO

Correction of the electromechanical counter

If a pulse sensor is installed in the gearbox to determine the mileage of the car, then to change the meter readings, the pros make a winding, which consists of:

  • Boards 1006VI1;
  • Two small ceramic capacitors;
  • Two MLT 0.125 resistors (if such resistors cannot be found, you can replace them with SMD type resistors);
  • One P2K switch;
  • Diode KD521 or equivalent capable of operating at a current of one ampere. This element will protect the winder if the polarity reversal of the circuit is allowed;
  • One terminal of the "mother" type, which is installed on the instrument panel instead of the speedometer controller. Otherwise, the electrical circuit will have to be cut;
  • wires.

The circuit itself is assembled as follows:

  1. Resistors are soldered to the board;
  2. Capacitors are soldered to the board;
  3. The board contacts are connected using jumpers made of wires. The conclusions to which the switch is connected are also soldered here.
  4. So that the structure is one piece and the wiring does not break off, it is wound with electrical tape.

Electric odometer correction

In this case, information about the distance traveled by the vehicle is stored in the memory of the microprocessor of the control unit. It is almost impossible to erase or change these indicators. Whatever number the odometer shows on the dashboard, when connecting diagnostic equipment, the real indicator will become known.

What is an odometer and what is it for

Correction of the odometer in this type of meters is carried out only if the instrument panel changes due to malfunctions of the shield.

How to make a corrector with your own hands

Since the odometer memory is not removable, to change the odometer parameters, you will need to disassemble the dashboard and remove the memory board. Basically, the memory is installed close to the microprocessor on the same board. The storage device is soldered. To change the data in its memory responsible for the odometer readings, you need to connect the microcircuit to the programmer.

It consists of:

  • Boards;
  • Three resistors (each of them must be designed for a resistance of 4.7 kOhm.);
  • The programmer is connected via COM output. This connector connects to the red or black wire. The main thing is not to confuse the poles. When connecting, you must remember that the red wire is a positive contact, and the black one is a negative one.

What else is needed to correct?

But it is one thing to assemble a programmer, another to connect it to a custom chip. This will require special software on the computer. Some experts use the Ponyprog program. True, this program does not work correctly on all computers. In this case, you can use its analogue.

What is an odometer and what is it for

Also, to correctly set the mileage, you will need a special software calculator. For example, the TachoSoft mileage calculator or its equivalent. By and large, this calculator translates the odometer values ​​(number) into a special code. It is in this form that this information is stored in the memory of the control unit.

The process of changing indications

With a suitable program and a designed programmer, you can proceed to the procedure for adjusting the odometer values. The sequence is as follows:

  1. The programmer is connected to the computer;
  2. Utilities are launched on the computer;
  3. In the Ponyprog program, the make, model of the car and the year of manufacture are entered. When you enter these data, a code with encrypted information about the mileage of the car, stored in the memory of the control unit, will appear at the bottom of the window.
  4. The mileage calculator starts. It contains the desired odometer reading. The utility translates this number into a hexadecimal code.
  5. The resulting code is entered into the drive instead of the previous code.
  6. After adjustment, the drive is installed back on the board. The shield is assembled in the reverse order.

If the flash drive correction was successful, the desired number will light up on the odometer. When performing such work, extreme care is required, since the microcircuit can be damaged during soldering.

How much does an odometer correction cost?

If the car owner has the courage to correct the electronic odometer, then the price of the issue depends on the cost of the elements from which the programmer needs to be created and on the availability of the software. With self-adjustment of mileage, there is a high probability of spoiling the odometer memory.

For this reason, this procedure should be performed by professionals with sufficient experience in such auto tuning. Depending on the region, the cost of odometer correction is from $40. Also, the model of the car also affects the cost of the procedure.

Using the odometer in determining the mileage of a used car

Since the odometer consists of two modules that separately show the total mileage of the car and the “daily mileage” (set by the driver himself to the desired segment, for example, to determine the distance from one point to another), the total mileage indicator will help determine whether to buy a used car or not.

What is an odometer and what is it for

When searching for a car in the secondary market, the odometer reading is a key factor in determining the “technical age” of the car (by years, the car may be fresh, but in kilometers it will show that the vehicle is pretty worn out).

Of course, in today's used car market there are a lot of copies with rolled mileage. In a separate article explains in detail why sellers do this. And here a list of models is provided, the mileage of which often does not correspond to that declared when sold on the secondary market.

If a model with a mechanical odometer is chosen, then everything is very sad here. Its design is so simple that even a non-specialist can rewind the mileage in such a way that it will be hardly noticeable. In such a situation, you will have to consider indirect signs of car wear and rely on the testimony of a test drive.

In the case of an electronic odometer, mileage roll-up is more problematic. To do this, you will have to intervene in the memory of the control unit. If the machine has undergone such cleaning, then the complete absence of errors is evidence that a professional has worked on the control unit. It is impossible that during the operation of the car not a single ECU error occurred.

For these reasons, you should choose a car with several control units, for example, so that there is an additional transmission ECU, ABS, etc. Often one error of a sensor is fixed by different control units. Therefore, computer diagnostics can reveal a discrepancy between the indicators of different ECUs

Related videos

This video shows how the odometer reading is corrected by outbid:

Mileage correction. How outbid twist mileage.

Questions and answers:

What do the numbers on the odometer mean? There are two scales on the odometer. One counts the total mileage of the vehicle. The second is called "daily mileage". There is a reset button for the second scale. This counter allows the driver to keep track of the local mileage. For example, some people, based on the mileage traveled, determine the time to refuel the car (in some types of LPG there is no sensor indicating the amount of gas left).

What is the difference between an odometer and a speedometer? The speedometer is a scale with an arrow (in the classic version). This device shows the speed at which the car is moving at a particular moment. When the machine is at a standstill, the arrow shows the minimum value (lies on the stop). The odometer measures the distance traveled.

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