I just decoded my engine warning light and found out that I have a faulty "rear heated oxygen sensor". How difficult is this to replace - tips/instructions?, price?? and is this something I need to replace asap?? Thanks for the help. PS this site is great!! Sure to have many more questions, Thanks again.

 

If the code cleared ok your O2 sensor is probably just a little dirty. Do a search on the board under "rear O2 sensor", or "0707" (that is the code you got, right?)
I get a code 0707 from time to time, but I haven't bothered to do anything about it yet. Some guys on the board say you just have to take it out and clean it with a bit of rubbing alcohol.

 

Changed mine a while ago but only after a few resets. If it does come on regularly you'll need a long 22mm open wrench (or a special oxygen sensor socket), some liquid wrench and a dictionary full of swear-words to yell while you get it loose... But once you do that it's an easy job. It's located just downstream of the cat (you can see a wire going into it if you look under the car). If you've got the tools and a couple of jackstands you can do the job inside half an hour.