I went to trade my car today and it was running fine. When the dealer brought it back, the CEL was on and he wrote on his appraisal report that the check engine light was on before he left the lot. (It was not) I immediately went to Autozone to run the codes and I got P0299 Turbo UnderBoost. I already searched and saw the endless possibilities that could be causing this. Is the dealer at all liable for things breaking on a test drive? He drove my car 6 miles metro during the test drive.

03 A4 1.8T Quattro
Thanks,