You fail one subsection you fail the whole thing. No one knows about subsection grading.
Anecdotally, people on here have reported passing despite believing they bombed specific cases by doing things like not finishing up the work-ups, etc. I’m not positive, but I believe some cases are experimental as well so if that were the case you can miss those. My advice regardless is to make sure you finish the diagnosis and work up section. If you’re someone who is pressed until the last minute, then quickly fill out the HPI/Hx/Physical and go do the diagnosis and work up and come back to polish off HPI.
Overall, no one knows how the grading within the subsection works and anyone who tells you otherwise is lying. There’s been no official published information outside of NBME STEP 2 CS PDF guide. All it says that isn’t common sense is that you can get dinged for ordering unnecessary tests and putting unsupported diagnoses so try not to shot gun, but on the other hand, you’re probably well off putting CBC/Electrolytes for everything but be as specific as you can.