A fuel level meter in a tank is a fairly simple mechanism that any car enthusiast with a basic level of technical knowledge can understand. Let's look at why the fuel level sensor does not work, as well as ways to eliminate all possible breakdowns (the needle twitches, "lies", shows only a full or empty tank).
Conditions for correct operation
If you have not previously encountered electrical devices and do not know how the fuel level indicating system works, familiarize yourself with the following concepts:
- variable resistance (rheostat) is a device with which you can adjust the value of resistance. The greater the resistance in the circuit, the less current flows in it;
- Fuel level indicator (FLU) is an element of the instrument panel that indicates the amount of fuel in the tank. Can be analog or electronic;
- Fuel level sensor (FLS) is a meter located in the tank.
Most systems for indicating the fuel level in a tank operate on the same principle. There is a float in the tank, on the counterpart of which there is a sliding contact. The sliding contact moves along a plate with contacts (resistive substance), rigidly fixed to the meter body. Moving the sliding contact changes the resistance value, thereby increasing or decreasing the amount of current passing in the circuit. The lower the resistance, the more current flows in the circuit and the more the fuel level indicator needle deviates.
The circuit includes:
The operating principle of a lever-type FLS is described, but in the case of a tubular-type meter, the difference is only in the method of changing the resistance in the circuit. Tubular type meters can be found on BMWs. In the new generation of VAZ cars and foreign-made models, the FLS is most often of the lever type and is attached to the plastic housing of the pump section. 
Warning lamp
One of the contacts of the low fuel level lamp can be attached to a rheostat. In this case, as the volume of fuel decreases, the resistance in the circuit drops so much that the current becomes sufficient to ignite the lamp.
In some systems, a separate thermistor is included in the lamp circuit (the resistance depends on its temperature). The thermistor is fixed in the housing of the pump section. When the amount of gasoline/diesel decreases to a certain level, it stops being washed and cooled by fuel. The passing current heats the thermistor, reducing its resistance. As the resistance decreases, the light on the dashboard begins to light up.
Malfunctions
For what reasons may the fuel level indicator not work:
- lack of good contact on any part of the circuit (breaking off wires, oxidation at the junctions of connectors, cracks at soldering points);
- malfunction of the instrument panel indicator (for example, broken solder joints);
- disconnecting the float from the sliding contact;
- fuse burned out;
- lack of contact between the resistive track and the sliding contact. The reason may be the formation of oxides and deposits on surfaces, weakening of the pressure of the sliding contact on the resistive layer, and abrasion of the tracks of the resistive layer.
The pointer is lying and works intermittently
Reasons why the indicator incorrectly shows the fuel level in the tank:
- the presence of additional resistance in the circuit (oxidation at the connectors, poor ground contact, formation of oxides, deposits on the resistive layer and sliding contact);
- Float casting defect, causing it to fill with fuel. Failure is extremely rare, but still possible, as is bending of the float rod due to mechanical impact during unqualified repairs;
- formation of deposits on the guide post (typical only for tubular type sensors). In this case, the movement of the float will be difficult.
The arrow always shows a full tank if the system has:
- the float has separated from the sliding contact (in this case, the slider will always be in the extreme position);
- the wire going to the indicator has a short to ground somewhere, which causes the resistance in the circuit to decrease.
A twitching arrow of the UUT indicates partial abrasion of the resistive track of the potentiometer. This will also cause interruptions in the operation of the pointer. Since the car is most often used with a fuel tank filled to 40-60%, it is in this range that abrasion of the resistive layer occurs most quickly. Therefore, the pointer can only work properly when the position of the sliding contact falls on an intact resistive layer.
DIY diagnostics
To find the reason why the fuel level sensor does not work, you will need a multimeter (we recommend reading,) and a control. The first step is to determine whether the cause of the breakdown is in the sensor located in the tank or in the indicator. To do this, remove the connector connected to the fuel section (located at the gas tank flap, which in most cases is accessible from the passenger compartment). Using the wiring diagram of your car model, determine which wire goes to the dashboard indicator. Turn on the ignition, then apply negative potential to the corresponding pin of the connector through the test lamp. If the pointer arrow quickly points upward, then the problem is in the sensor. For further diagnostics it is necessary to remove the fuel section. A multimeter will measure the resistance of the potentiometer.
The constant presence of a small canister of gasoline in the car or the car owner voting on the highway with a request to refuel, all this is a consequence of the fact that the fuel sensor in the car does not work. The breakdown of this sensor does not affect the operation of the main mechanisms of the iron horse, but it significantly affects the comfort of using the car, since there is always a need to calculate how much the car has traveled since the last refueling and how many more kilometers can be driven without stopping at a gas station.
Author of the article: mudriy_lev
Specialization: repair of auto generators and servos in cars.
Place of work: service center. Experience: 2 years.
Education: higher education - electrical engineer, secondary specialized education - mechanical assembly mechanic.
Let's look at the main reasons.
Modern cars are equipped with a wide variety of fuel level sensors. The widest niche has been occupied by sensors based on potentiometers. This type of conversion of fuel level information into an electrical signal has many advantages.
There are two types of sensors based on this method of measuring fuel level:
- lever (widespread)
- tubular (used mainly on large vehicles)
If the lever-type fuel level sensor does not indicate the fuel level correctly, the reason associated with the potentiometer and causing this malfunction may be as follows:
- Potentiometer contacts have oxidized
- there has been natural wear on the tracks or slider of the resistor
- natural aging of the resistor
- resistor does not match the nominal value
Potentiometer Diagnosis and Troubleshooting
A symptom that the potentiometer contacts have oxidized is a temporary lack of accurate information about the fuel level in the gas tank. The owner notices that from time to time the indicator shows reliable information. Usually, in this case, the light indicating the end of fuel works flawlessly.
To diagnose this malfunction, it is necessary to visually inspect the variable resistor of the fuel level sensor. The oxides will appear different from the normal color. Based on their number, a decision is made on what to do next:
- clean (in case of a small amount of oxides)
- move the slider (if only part of the tracks are oxidized)
- replace the fuel level sensor with a new one (if the oxides are significant and have led to damage to the tracks or slider)
A symptom of natural wear of the tracks and runner is either a complete failure of the sensor, or its correct operation only in certain areas. A visual inspection in this case shows that the tracks are worn out, and in more rare cases, damage to the runner.
If it is possible to move (bend) the slider to an undamaged area, the sensor will please the owner with its long-term, proper operation. But if the runner is damaged, or the tracks are seriously damaged, repairs do not make sense. It is necessary to purchase a new fuel level sensor.
To establish the next reason why the fuel sensor does not work, you need a multimeter or an ohmmeter of any design. A resistor can change its resistance and, as a result, display unreliable information. Checking the resistance value with an empty, full and half-filled gas tank will help identify this problem. Repair in this case is not advisable, since it is safer to install a new sensor.
If problems with inaccurate fuel level arose after installing a new sensor, then a common cause is a resistance mismatch with the nominal value. This situation arises due to the fact that the sensors are similar in appearance, but their different modifications have different resistance values.
The float is not informative
Problems when the fuel gauge does not work are often related to the float. There are 2 types of floats installed on cars:
- hollow (plastic, plastic, metal)
- made of lightweight porous material
The first type of float faces the problem of mechanical damage. As a result, the indicator needle gradually does not reach the maximum when the tank is full more and more. The float fills with gasoline and the gasoline sensor shows the wrong level more and more every day. Repair in this case is carried out by replacing the float.
The second reason why the fuel sensor is lying is encountered by both types of float. As a result of mechanical damage to the gas tank, the float becomes jammed. In this case, the indicator will show either a single value or work only in a small range. Elimination of this breakdown is possible only by replacing the gas tank.
"Conscientious" previous owner
There is no point in monitoring this type of “fault” on devices. If the car was just purchased on the secondary market and the fuel level sensor does not work in it, you need to remove the fuel pump and look for the presence of this sensor. There are cases when this sensor (or part of the sensor) is simply missing as a result of “pre-sale preparation” by the previous owner.
The sensor does not indicate the fuel level correctly due to bending of the lever
The main sign of such a problem is that the indicator needle does not reach one of the extreme marks. Elimination of this malfunction is carried out by editing the lever. But since such a malfunction does not appear on its own, but is the result of a mechanical impact on the gas tank, the float may jam after adjusting the lever. In this case, repair or replacement of the gas tank will be required.
Indicator and its problems
Also, the reason why the fuel sensor does not work may be hidden not in the sensor itself, but in the indicator, which shows an incorrect fuel level as a result of the movable winding of the indicator being wedged and, as a result, the impossibility of its free movement.
The operating principle of internal combustion engines is based on the combustion of a fuel-air mixture. Engines that use diesel and gasoline have become widespread. It is important for a car driver to understand how much fuel is in the tank, how quickly it is consumed in a particular driving mode, and how many kilometers the car can still travel before refueling. To inform the driver about the fuel level, there is a corresponding scale on the instrument panel. Data is transmitted to it by a sensor located in the gas tank. Like any other element of the car, it has typical malfunctions, and the driver needs to know: how to diagnose them, fix them, or, in extreme cases, replace the fuel level sensor.
How is the fuel level in a car measured?
The interaction between the fuel gauge and the fuel sensor is based on the transmission of a signal, which can be analog or digital. Depending on the type of signal transmitted, fuel level sensors differ.
In modern cars, digital sensors are most widespread, which are much more accurate than analog variations. The digital sensor receives analog information about the fuel level, which is converted into a signal and then transmitted to the indicator. In this case, the value that comes from the sensor is calculated based on the geometric parameters of the fuel tank and taking into account the correction for uneven distribution of fuel throughout the tank.
The float, which is a digital potentiometric device, is directly responsible for measuring the fuel level in car tanks. It is made of light materials (plastic, foam, light metals) in order to be constantly on the surface of the fuel, thereby transmitting readings to the sensor. Such a system for measuring the fuel level in a tank is simple, reliable and inexpensive, which is important for mass production of cars.
Float sensors can be divided into two types:
Tubular fuel level sensors are considered more accurate than lever ones. The advantages of the tubular design are especially evident when the car is moving uphill, downhill or on turns, when the fuel level in the tank fluctuates and the lever system can read incompletely reliable indicators. At the same time, a tubular fuel level sensor is more expensive than a lever one, and it may not be installed in all fuel tanks due to geometric shape limitations.
Malfunctions in the fuel level indicator
The main symptom of problems with a car's fuel level sensor is false data entering the indicator. Based on the “behavior” of the pointer, we can draw some conclusions about the malfunction that has occurred:
According to traffic regulations, operating a vehicle with a faulty fuel level indicator is prohibited. Based on this, the problem should be corrected, and most often this is done by replacing the sensor.
How to remove the fuel level sensor
Depending on the car model, the process for removing the fuel level sensor may vary slightly. In this case, we can highlight the main points that you need to pay attention to in order to remove the fuel level sensor:
When all the manipulations described above have been completed, the fuel level sensor can be removed. This must be done as carefully as possible so as not to damage its structure.
How to install and check the fuel level sensor
Installation of the fuel level sensor is carried out in the reverse order of removal. It is important to remember some basic recommendations for installing and checking it:
- Before installing the sensor, it is necessary to clean the seat, including traces of old sealant, if it has been applied;
- Install a new gasket into the seat, having previously lubricated it with sealant, if required;
- Check the operation of the fuel level indicator. To do this, after installing a new fuel level sensor, you should not immediately block access to it. After driving about 50 kilometers, you will need to inspect the fuel sensor and make sure there are no leaks.
Correct readings from the fuel level sensor allow drivers to plan their route, which is especially important for long trips.
Probably many people have had to face the question: why doesn’t the fuel level sensor work? And the following situation also happens: after starting the engine, the sensor shows that the tank is empty, and while driving, the value on the sensor reaches the desired level. The following option is also possible: the needle is stuck at zero, but in fact there is still half a tank or the values on the dashboard are constantly changing. It can be very difficult without a sensor working properly, especially on long trips. You need to constantly keep in mind the moment of the last refueling and its volume, and keep a canister of fuel in the trunk just in case. Due to the mass of inconveniences caused by one sensor, we will look into the problem in this article. Why doesn't the fuel level sensor work? What is the reason for the breakdown? In this article we will try to describe possible options for sensor failure, as well as the reasons for the failure in readings. The most commonly encountered sensor can be considered potentiometric. This prevalence is due to its simplicity, low cost and clarity of the obtained values. However, it also wears out very quickly, and oxidation of the tracks is possible. Due to the high prevalence of this type of sensor, we will consider possible failure problems using its example. Sensor readings fluctuate The reason for inconsistent sensor values is wear on the contact tracks on the board. The tracks wear out due to the constant impact of the fuel sensor slider. One option to solve this problem with minimal losses is to bend the slider so that it is higher than the worn-out area on the board. However, if a significant area has been wiped, then tucking the problem will not solve the problem. In this case you need to replace the sensor with a new one. Before replacing the sensor, you need to study the instructions and read there information about its resistance. This is very important, because for one brand of car there may be sensors with different resistances, and if you install an indicator with an incompatible resistance, it will be very difficult to navigate the readings. The best option is to remove the old device and take it to the store. The fuel level sensor is lying The fuel level indicator can either underestimate or overestimate the practical values of the amount of fuel. With such symptoms, adjusting the sensor may help. There are two types of adjustment for this type of malfunction.
- First: we move the float pin to two extreme positions, while the arrow on the indicator should also fall into the two extreme positions 0 (empty) and 1 (full). If in the extreme position of the pin the arrow does not set to “0” or “1”, then it is necessary to bend the pin so that it remains movable and adjust with the bent axis;
- Second method: disassemble the instrument panel and get to the fuel level sensor itself, remove the arrow from it and reconnect the wires to the sensor. Start the car and let it sit for about 10 minutes. Then set the pointer axis to the extreme position “1” and connect the pointer.
If the sensor is stuck at “0” You need to disassemble the dashboard and again get to the fuel indicator, find the contact wires going to it. There will be nuts that need to be unscrewed, cleaned with sandpaper (to prevent oxidation) and put back, tightened tightly. It is also necessary to inspect and clean all the masses on the body (special attention to the mass under the handbrake). With this problem, it may also be possible that the float gets stuck in the tank. Well, as the most common option, the fuel level sensor fails. How to find out: the problem is in the sensor itself or the indicator? We take a multimeter and measure the resistance on the sensor (checking the indicator): - if the tank is full, then the approximate resistance value will be about 7 ohms or less;
- if about half the tank, then the resistance ranges from 108 to 128 Ohms;
- if the tank is empty, the value on the multimeter will register approximately 315 to 345 ohms.
Sensor check: - disconnect the wires going to the sensor;
- connect the resistance (R=330 Ohm) and add a resistor (R=10 Ohm) to the series circuit;
- start the car;
- We begin to change the resistance on the resistor with the slider: from 0 to 10 Ohms;
- the arrow on the sensor should float from “empty” to “full”.
Having started my journey as a trader in 2008, I began to read everything I came across about trading systems and trading on the stock exchange. I tried one system after another. And not a single system gave me a stable result. At first I blamed myself for not always following all the rules exactly, not always doing everything according to the rules. When I became more disciplined, the situation did not change much. As before, the result was far from expected - I was already earning money, but still this earnings were rather accidental. Because I didn’t understand what I was doing. I acted in a formulaic manner, did exactly what the books said (so it seemed to me), but I did not understand the market. I didn’t understand why sometimes the same signal/template/pattern gives profit, and sometimes not. Why, while doing everything right, my earnings are far from expected. Over time, I abandoned templates/patterns. Refused all indicators. Because they prevented me from seeing what was really happening in the market. It is very difficult to make money by acting in a stereotyped manner. Each situation must be considered separately. After this, the results changed radically. When I started teaching trading a few years ago, I saw that most people faced the same problem. Everyone is trying to act in a pattern. Another problem turned out to be that all information coming to us passes through some kind of brain filter. Something remains, something is eliminated, and something is transformed (!!!). What happens as a result: the brain from the working system tries to form patterns, and even slightly different from the original ones. Do you think it’s possible to make money using a system that has undergone a huge transformation in your head, and is also limited by patterns? It may be possible, but it will be far from the system you were taught. And, if the situation with incorrect perception can be corrected during training, when you have a good mentor and he watches what and how you do, then it is very difficult to get rid of stereotypes. What is the difficulty of algorithmizing trading systems? Although the situations are similar, they are all different. Just as you will not find a single identical leaf on a tree, you will not find a single absolutely similar situation in the market. But at the same time, you can determine the name of the tree from the leaf.
What is the pattern? For example, on the M5 chart you see a good sell signal. The trend is down, the price rolls back to the relatively strong level of 41.3, there is volume, can I sell?
and what the situation on H1 might look like:
We see that the price has hit the level of 40.78 on the hourly time frame and is going up. The level was maintained, there is global growth (at H1). Is it possible to sell against a level on a higher TF? Theoretically - yes. But with confirmation. Let's see what happens next, on M5:
we see prices rising. Those who want to work with the downtrend will most likely receive a stop. Although the price was falling throughout the day, it made a good pullback to a good level, and even volumes appeared at this level. Those who see the level on the watch will sell only with confirmation. Without seeing this, a buy signal appears at the level of 41.24, immediately before the breakout.
How long to keep the purchase? After all, there is an upward trend on the watch, and it is already obvious on the M5. In addition, the maximum of the day has already been broken on M5. Does this mean we will continue to grow? Can I buy more?
If you plot the flat hourly level on m5, the picture looks like this: 
We have broken through the level of 41.8. But what kind of breakthrough is this? This is a false breakout. This means that the long profit goal has already been achieved. And you CANNOT make purchases!!! And even vice versa, we can look for a sell signal. Buying before a level is done only when you want to work on a breakout. But again, this can only be done under certain conditions. NOT IN THIS CASE!!!
What follows from this? You can't achieve good results by doing everything in a formulaic way. To trade successfully, you will need to analyze several charts with different time frames at once. But by doing this, you can get ahead of the situation. By the time most people see a trend, it's probably already over. Therefore, by assessing the situation as a whole, you can enter at the beginning of an emerging trend.
Is it possible to work from levels? Can. If you know how to identify them and how to work from them. Is it possible to work from all levels? If you want to make money, you must select your levels very carefully. Working from all levels you will have a lot of stops. By assessing the situation comprehensively, depending on how the price is calculated with the level, you can choose 1-3 levels per day, from which you can get a good result.
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