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Discussion Starter · #1 · (Edited)
I have been having some issues with my vehicle's fuel gauge. I own a 2004 E46 Sedan. The fuel gauge has been giving me incorrect readings for some time. For example, the gauge needle would show a certain reading when I turn off the engine. Then, after some time, when I restart the engine, the gauge needle would show more fuel than what was in the tank at engine shut-off. Also, after driving the car for a few miles, the gauge needle would drop by more than a gallon. This is clearly unrealistic, because the car would never consume a gallon or more of fuel in just a few miles under normal driving conditions. Moreover, as the fuel gauge needle got closer to the half-level mark, it would get stuck in that region for some 60 or so miles of driving before it would move past the half-level mark.

After lots of online research, I have narrowed down the cause of the problem to the fuel level sensors. I understand the E46 fuel tank is divided into two parts and there is is a fuel level sensor in each part. It also appears that the left sensor is more likely to malfunction than the right one. I have also found out that I can check the readings from both fuel level sensors using the test function 6.0 on the on-board computer. I am trying to determine whether one or both of my sensors are going bad. Now, I have several questions that I am hoping someone here will be able to answer:

1. The left sensor reads 24 liters and the right sensor reads 33 liters when the tank is completely full. When the tank is not completely full, is it normal for these readings to fluctuate even if the vehicle is standing still and the engine is turned off? When my fuel tank is not full, both readings fluctuate while the car is standing still and the engine is off.

2. It is my understanding that the left side of the fuel tank goes empty first. When that happens, should the left sensor reading be 0.0 and not fluctuate at all?

3. This is actually tied to question number 2. If the left sensor gives a non-zero reading when the fuel level is less than half a tank, does that mean the left sensor is going bad?

In case you are wondering, the car is actually still under warranty and I have already taken it to the local dealer about this issue. The dealer told me both fuel level sensors were replaced to fix the problem but the erratic behavior of my gauge is still there even after this so-called repair. I think the dealer did not do anything on my car and they lied to my face. So I have decided to never go back there. The next closest dealership is about 150 miles away and there is no guarantee they will fix my problem. I plan to take my car to a local independent shop eventually and get the problem fixed there once I have a better understanding of what's going on.

I will greatly appreciate any useful information anyone can provide.
 

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Ubergeek
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First of all, I'd keep taking it back to the same dealer. If you think they lied, mark the sensors. I think they're easily accessible from under the rear seat.

I don't think the sensors should read the same when the car is sitting still. Which sensor reads more depends on which way you turned before you shut the car off. If you turned left, more fuel probably sloshed into the right tank and vise-versa... that is, if the fuel tank doesn't have tubes that connect the halves on the bottom of the tank. I'd like to see a picture of a fuel tank cut apart myself since I experience fuel starvation turning right when autocrossing with less than half of a tank.
 

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Fuel lvl.

I think I had a problem after getting the car out of winter storage with fuel indicator not reading correctly.

I ran two tanks of fuel with BMW fuel additive and no problem. I've since added another bottle and I'll probly add a bottle to a full tank when I put it up this winter for a time.

It is rumored this helps the sensors. Hope so...
 
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