04, X3 Fuel Level Sensor

[bostongrun]

I have an 04, X3 with 133 k. For a while the fuel gauge has been slow to rise to full after adding gas. My wife recently ran the car out of gas. After refueling I observed that fuel gauge will not go pass the 1 O'clock position (slightly above 1/2 ) even though I know it is topped off with 18 gallons. I believe one of the two fuel sensors is the culprit. I have read a lot about ethanol and bad gas being the cause. Techron fuel additive even addresses fuel gauge corrosion on their sales page. So I put some in and will wait for a few days but I am not betting that will cure it.

There are actually two fuel level sensors each costing $105, they don't look to hard to install but does anyone know how to determine which sensor is the culprit. Unfortunately, they are different parts and not interchangeable. Has anyone had this issue ?

The two sensors are variable resistors as the fuel level rises the resistance goes up to 400 ohms per side. I am assuming that because they are in the same linear series circuit that 800 ohms of resistance is converted into an analog value represented by the gas gauge. My guess is that because the onset of this problem was incremental as opposed to abrupt that it is not a mechanical failure e.g float fell off .

Another assumption, could this be remedied by gently cleaning (pencil eraser) or chemically cleaning the contacts on the contacts on the rheostat ?

Any help would be greatly appreciated ,

[bmwdirtracer]

There are instrument panels self-tests on all newer BMW's. The process for calling them up varies, from model to model. You can Google "BMW Instrument cluster self test", and find lots of entries.

Here's for an F10:
https://www.youtube.com/watch?v=n4e_kaY4E0I
Here's for an E46 (closer to yours):
https://www.youtube.com/watch?v=IyhzbSOcqJI

There are more. Sorry, I don't use these, because I have diagnostic computers which tell me most or all of this information. But I'm pretty sure you can use these self tests to determine which side of the tank is reading incorrectly.