Nissan Repair: 1998 Nissan Maxima, oxygen sensors, nissan maxima

Question
Hi - my service engine soon light was on, and my mechanic got two codes - PO325 and PO153.  He said the PO153 code is for all four oxygen sensors.  Help - does this mean that all of these sensors need to be replaced.  He gave me a price of $175 for each oxygen sensor, for a total of $700, and said the knock sensor would be $200 just for the part.  Thanks for whatever info you can give me.

Answer
Mary,

It is about time to get these replaced.  But, I am cheap and do not like to spend money.  Check out rockauto.com for the parts or courtesyparts.com and you can save a bundle on the cost on these parts.  If you could find someone to install them you could save even more.  The knock sensor is the only one that is a pain as all four oxygen sensors only require a 22 millimeter socket and or wrench.  The knock sensor requires the intake be removed to gain access.