My first codes about a year ago where for connection on the secondary o2 then fuel trim and primary o2, yesterday the car add no code, the fuel filter was over due by 40.000 miles. I couldn't feel any bad idle so I didn't think of any vacum leaks,the fuel trim and o2 codes did give me the impresion that of a low fuel to air ratio and the Egr valve came to mind since the code came on only after some fair amount of driving and the codes is a Emmission one, the valve wasn't replaced. I'll resend the secondary o2 that I ordered and I am all the wiser for now. the car been this young now I figure the o2 must be due for renewal for the fuel injection to work correctly, my privious car, 84 Audi 5000 285,000 miles had the o2 light come on every 40,000 miles or so and just add to reset the switch behind the dash, changed it only once, I'd figure it be simular. I am going to need SDS to read the values next time If I sense it really needs it, so far everything on this board has help to narrow it down without extensive equipements and thanks again.