If you got the codes, GT1 isn't really going to help all that much. What are you specifically looking for?
P0171 could be multiple things. I've been chasing mine for weeks but has gone out on its own.

Position sensor might just be dead. Mine was and I replaced it, code immediately when out. But I am getting a feeling you don't think it is a CPS.

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2011 E70 50i M Sport