Audi Repair: O2 sensor for 2002 A4 3.0 Quattro, ski masks, oxygen sensor

Question
My check engine light is on.  Failed smog. Dealership says problem with oxygen sensor and check valve and that it will cost $1035.00 to fix. Don't have that kind of money in my sock and I'm fresh out of ski masks. Can you talk me through the self repair or a more reasonable solution? The dealership also said there are 9 other things wrong with the car with a total of $3320.00 to fix. Help!!!!!!!!!

Answer
Ask for the printout of the codes that the dealer is referring to;   Any autozone will check the codes for you also.  Cross reference them.  An oxygen sensor is around $100 each.  Typically the front ones go bad first; they get hottest.  Let me know what the other engine fault codes are.  Jan