Nissan Repair: 98 Altima GLE, codes PO400 & PO325, courtesyparts, cheap sources

Question
Hello,
My car cut off while I was driving. When I had Autozone do a test the codes PO400 &  PO325 gave me at least 9 different probable causes. Is there anyway I can narrow this down by looking for other clues? I don't want to pay a mechanic for all these possibilities. I can also tell u that another motorist a few months ago noticed excess smoke coming from my exhaust and he suggested I get the sensors checked. What kind of cost am I looking at if it is indeed the sensors and/or the EGR system?
Please advise. I don't want to spend too much I'm currently trying to sell this car. Thank you in advance.


Answer
Rocki,

Replace the EGR valve and the Knock Sensor and reset the code.  A wrecking yard might be a source if you are trying to save money on parts.  You just want the thing to run, not have codes and pass smog.  Used parts work as good as new ones.  They might not last as long, but they work just as good.  Also, rockauto.com or courtesyparts.com are good and cheap sources for purchasing new parts on-line.  About half the cost of the dealer.