Again, we need to know if you have the MID or the Navigation screen??? You can change the scale from liters to gallons...easily...but I can't tell you how if I don't know which set-up you have...MID or NAV?
When you say "checking out the TEST"...are you talking about UNLOCKING your OBC to access the 21 TESTs? If so, if you didn't go to TEST 19...then the OBC is still LOCKED...thus that's what you will see if you try to access any of the OBC TESTs other than TEST 1 or 2.
Where are you getting your information from to UNLOCK your OBC? If you don't have complete information...then wait until you do so that you don't reset something you don't want to reset. This feature wasn't intended for the consumer...but is a way to access the input/output/functions of the IKE (instrument cluster electronics).
Here's the instructions on how to UNLOCK your OBC and a brief description of each TEST:
Below is the procedure for unlocking the OBC (just like the link above) and there's also a brief description of the OBC TESTs. Disregard that it mentions "e38" in the heading...the "unlock" info applies to the e38/e39/e53 with the high instrument cluster...the low instrument cluster used in the e46 & e53 is similar except there's only 1 button on the cluster, so initiating the TESTs is slightly different as well as how they appear in the display since the low cluster doesn't have the larger 20-digit alpha/numeric display: