seller filled the 02 C5 up with regular and is telling me not to worry bout the CEL and the code as soon as I put high test in it will even out and the code will go away.
Do I need to be concerned I can't go to inspection with the CEL on:thumbsup:

I had P0171 (fuel trim system lean bank 1) and P0174 (fuel system lean bank 2) when I had a bad fuel filter on my 2002.
I do not think yours is because of the gas but I am not a mechanic, I think P0171 means low pressure on one of the fuel rails, have you checked for leaks?
Mike

no don't know an easy way to do that I'm a novice with the car. Filled it with premium today, cleared the code but it came right back on.

Have a look at this link.

http://www.obd-codes.com/p0171

thanks I'll try cleaning the MFA thats seems a likely place to start