Repair by parts replacement does not work, it's expensive, time comsuming and risks introducing additional problems especially if you muck up settings and sdjustments in the process. STOP REPLACING PARTS. Figure out the problem then repair by adjustment, replacement whatever. I can strongly urge that you get away from your car for a while and invest some of your time and intellect reading the 700/900 FAQ sections. It is an excellent education on the ways of our Volvos. The answers to your questions about codes and the use of the inbuilt diagnostics and much much more are all there. Why ask for someone to type it out for you again. If you have questions after that Bricksters here will smother you with help, sympathy, encouragement.