The fuel gauge does not show well: how it works, problems and solutions

There are manufacturers that in some models dispense with certain information in the clock or instrumentation panel. It's not hard to find cars that don't give us an engine temperature reading beyond a blue or red LED for situations where the engine is hot or cold, respectively. In the same way, we also find cars without a rev counter. What has never been missing, nor will be missing, is a fuel gauge.

This can be a clock with a needle that moves inside or a digital graphic. Its function is very simple, but essential. It indicates the amount of fuel remaining in the tank and warns us, through warnings or the classic reserve light, that we stay in a ditch with the car stopped, without fuel. The fuel gauge, like any other element of a car, can cause problems.

Most common fuel gauge faults

The fuel needle does not go down

The reasons can be very diverse, but in analog meters the most common is that the needle may get stuck in a certain position. The most normal thing is that the gasoline needle does not go down because has run aground at the maximum, or that it does not rise because it has risen at the minimum.

The fuel gauge does not read well

Also you might have a drift and mark up or down from the actual amount of fuel in the tank. That is to say, that it has been misplaced from the turning range that it has to do and always marks improperly. It is also possible that the clamp to the axle has become loose and slides down a little with bumps or strong vibrations.

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The fuel gauge needle goes up and down.

Sometimes it also happens that the needle “dances” in a series of rapid fluctuations of the fuel level. In other words, that it moves frequently with curves, speed changes and unevenness. Something that happens when a retarder system has broken or dislodged, so that the movements of the gasoline fuel are transmitted directly to the dashboard.

Do not forget that the gasoline or diesel fuel in the tank it moves and forms waves with each swing, so the buoy moves continuously. If there is no mechanical or electronic element that keeps the needle stable and with slow changes, we will only obtain a measurement stopped or at a constant speed and on the flat. If the pointer moves like this when stationary, the fault is usually in a sensor.

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What is a fuel gauge made of?

So that you know how to locate the problem, you should know what the fuel meter system is like. It is made up of two main elements: on the one hand the clock or chart indicator and on the other the pump sender of gas. This last element is a buoy that floats and is connected to a potentiometer. According to its position, it gives a reading to the indicator of the box.

If the fuel needle drops faster or slower in some areas, it does not necessarily indicate a malfunction of the fuel gauge system. The deposit shapes are responsible for these behaviors. For example, it is common for the needle to last many kilometers pointing to the maximum after filling a tank to the top. This happens because from the highest position of the buoy to the fuel inlet, the gauge will always remain in the highest possible position, thus indicating maximum filling.

It is also not a malfunction that the level varies if the car is located on a slope. These conditions cause the fuel to move, and therefore the float point of the buoy, which can lead to an erroneous reading. In the most modern cars, the vehicle has to spend a while in these inclined positions to show the reading, sudden changes of short duration do not usually affect the system, which knows how to interpret (up to a certain limit) these situations.

As in the oil pan, the fuel tanks usually have a series of walls or shapes inside, to prevent the fuel from moving excessively in the curves, which can lead to the pump going unprimed and the car jerking due to lack of fuel. These walls are also the ones prevent the level meter from giving an erroneous reading on curves, since as the fuel moves, the position of the fuel gauge and therefore its reading varies.

Why does the fuel gauge fail?

the fuel gauge can fail for several things, that is why there are many models that tend to show this defect over time. For example, some older generations of the Audi A4, the Citroën C3, the Renault Clio and Megane or the Seat Ibiza, to name a few. Although any car is susceptible to a breakdown of this type, if you are unlucky.

Having seen the aforementioned points, we have to start worrying if we see that the gasoline clock does strange things when we drive normally. Variations on slopes or sharp curves can be left as part of normal operation, at least in older cars.

If the needle does not move from the home position and the reserve light does not work, there may be several causes. The electrical circuit may be cuteither physically due to a broken cable or by a blown fuse, as well as a lack of mass. The first thing to check is how easy the fuse is. Also, a fuse kit is very cheap And it takes up almost no space in the trunk.

To do this, you can locate it with the car manual, although it can also be indicated on the fuse cover. Once you have it you can check it visually or, if you want to make sure, use a multimeterBecause They are very cheap. The steps to follow are:

• take out the fuse with the car off and the key removed.
• Set up the multimeter to measure continuity. That is, turn the mode selection wheel to put it on the symbol of a speaker or an arrow with a vertical line at the end.
• Put the test leads of the multimeter both ends of the fuse.
• If it doesn't signal is that the fuse has blown

It is also possible that the gauge itself is faulty, or the fault may come from a faulty fuel gauge.

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Conclusion several open fronts, so they will have to be discarded gradually by carrying out the pertinent checks. The smartest thing is to start with the most probable or, at least, the easiest to review.

Si the gas level fluctuates a lot Under normal conditions, it is possible that it is due to a problem of incorrect mass or also to the fact that the tank may be deteriorated and some of its internal containment walls may have detached, giving rise to greater movements of the fuel.

This problem can also be caused by some electrical problem of the gauge or the clock itself, as well as a physical problem with the gauge buoy, which could get stuck due to accumulated dirt. If the problem is with the reserve light, which does not come on, the bulb in the clock panel may have burned out.

In the event that the problem is that the clock gives a fixed reading, regardless of its position, the fault may be in a stuck gauge or in a defective gasoline gauge. The interesting thing about some models, is that it can access tank through any opening, without the need to remove the fuel tank. For example, from under the back seats or in the trunk. Although this is usually found more frequently in older models.

How to repair the fuel gauge?

This task can be complicated. The first point is detect the source of the fault, which, as we have seen, can have very diverse origins. Once the problem is located, the problematic part will have to be replaced.

Check fuel gauge

We can start trying to rule out a mechanical or electrical failure of the panel. For this we will bridge the two contacts of the gauge (or putting the positive to ground) and we will check if the level of gasoline rises to the top. If it marks the maximum, the problem is not with the control panel or its wiring. On some vehicles with voltage limiters this check system may not work.

check potentiometer

If this part is correct we proceed to check fuel gauge potentiometer (fuel level sensor). To do this, follow these steps:

• Set up the multimeter to measure the proper resistance range, which is indicated by the Greek letter Ω. In this particular case you have to turn the wheel up to 2 kilo ohms.
• drop the wires that go to the gauge
• Place the test leads of the multimeter in the places where the cables were placed.
• While the test leads are in place, go moving the gauge hand up and down
• If it works correctly a linear and consistent change should be observed of the resistance measured by the multimeter. For example, a smooth step change from 33 ohms to 213 ohms.

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If you see that the fuel gauge is malfunctioning, you can buy a new one for prices that usually vary between the 30 and the 60 euros. Although if your model is premium, the price can go up to 100 euros or even more.

Another test that should be done on the fuel gauge is the voltage that reaches it, which must be 12 V.

How much does it cost to repair the fuel gauge?

The price will vary depending on the defective item. If it is a cut cable, a bad ground or a fuse, the repair can cost a few euros if we take it to the mechanic, or nothing if we do it ourselves. If the source is the gauge, it will be necessary to see if a cleaning solves the problem or if, on the contrary, there is than replace the entire assembly or even the reservoir pump (about 200 euros).

The problem can also lie with the tank itself, which would be a more expensive repair if a replacement is required. If the gasoline clock was the origin of the problems, it would be necessary to see if that reference is sold separately or if, on the contrary, it is necessary replace the whole watch box, which can have a considerable cost.

Images 4, 10 and 11 – Sean MacEntee, Tony Edge, Brian Shamblen

More information about this model

Renault Mégane

• Plazas 5
• Power 116 - 300 hp
• Consumption 1,2 - 8,5l/100km
• Assessment 4,5