Thanks ya'll thats great info and i will hit the dealer up tomorrow. Happy easter again and take care.

 

Im getting ready to replace my front 02 sensor--Ive been reading the Front sensor is the one that has to do with AF and your gas mileage? The second one after the cat just monitors your cat condition. SO Im just going to replace the front one for now. My Runnner-99 has 80K+.

My dealer wnats 242 bucks for 1, I have the Cali. model but damn that is spendy.

 

I don't know which sensor does what, but I got my problem taken care of by just replacing the nuts and the gasket of the front one that fell out. As a side note, 242 dollars is a little steep, maybe someone on here knows where to get one for a little (or a lot) less.

 

Give the guys over at URD a try, I'll bet it's quite a bit cheaper ($170 or so):
http://www.urdusa.com/product_info.p...s_id=430006000

 

Yes you are correct-171 bucks for my Cali model, oh lucky me

Do they come with the gasket do you know? Ill ask them tomorrow when I order it.

 

I just got my front A/F for my Cali. emissions '99 4Runner from URD; the gasket was in the box. I can't imagine why people are saying to do both front and back at same time. The back one gets much less thermal abuse, and as stated above, its functionality is much less important. It will probably outlast the front by quite a bit. There is no pairing aspect to these parts.

 

What is the average life-expectancy on the pre-cat O2 sensor?

My 2002 4runner is just above 50k, and the CEL came on today, throwing an O2 sensor related code. Seems like these don't usually get replaced until 60k-90k and I'm curious if mine is prematurely going out because of some other factor.

Any thoughts?

 

That sounds a little early but you never know! I have read change the front one out at 75K, I have 93K on my runner with no CEL ever but Im replacing it anyway cause my mielage has taken a big hit