Test #6 in the hidden menu shows the tanks levels, as Andrew has stated.
If you have a high cluster (variable text message along the bottom of the cluster), watch this to learn how to access the hidden menu: -
https://youtu.be/tdVrXp_RQGk?si=h1AcUl2mIruPggBN
If you have the low cluster, there is a slightly different process: -
https://www.bimmerfest.com/threads/h...luster.432740/