Diagnosis Problems: What to Do Next

Hello everyone!

A friend performed a diagnostic check on my 1999 1.9 TDI Sharan and tried to reset the service interval indicator.
Since the error reading, my fuel gauge is showing zero, and the low fuel warning light is constantly on, even though there's enough fuel in the tank. What could be the problem? Is it a faulty instrument cluster, or could it be related to misaligned fuel lines, as I've read about in this forum?

I am grateful for any advice!

Best regards,
Michael.

Your buddy is messing around and then leaves you stranded? That's great . *He* should post here, because he knows what he changed. A simple error reading shouldn't have such effects. (I'm just assuming he's using the correct tools).

EDITED:
With so little specific information, you won't get any useful answers: part numbers, which tool, versions, is it registered?, what has been changed, etc.