'99 C230 ce light and low gas light flashing
 

'99 C230 with about 86,000 miles:
The check engine light is on and the low gas light will begin flashing after about 10 minutes of driving. I took it in and they pulled off code P0170 and then all they did was reset it and said no code was pulled off after that so everything was fine. Well that obviously is not the case because it came back on a day later and is doing the same thing. The car seems to be running fine other then that, no hesitation or rough starts.
Does anyone have any suggestions on what might be wrong? Thanks!