I'll try that if the problem comes back. I've gone through a couple more tanks and the level sensors have been working fine. The main issue seems to have been the installation of the left side level sensor. It needed to install it at a slight angle, with the bottom centering feature tilting towards the back of the vehicle. Maybe something happened to this X5 in it's 120k mile life that messed up the left side tank. From what I've read, the level sensor is supposed to get installed straight-down and not at an angle. If I do install it straight down, it reads incorrectly when the tank gets low and seems to get stuck.

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2001 x5 4.4 125k