Well I recently bought myself an evo 8 which was in really good condition for the price. A few days ago the o2 sensor failed, I got the codes po171 (system too lean), and po134 (sensor circuit no activity). Now I'm no mechanic, but I do understand most of how these cars work (I still get my work done at the shop however). I'm worried that this o2 sensor failure could be because of a bigger issue since I just bought the car. Do 02 sensors break from time to time, or are they usually a sign that something else is wrong? I could really use the help.

 

O2 sensors fail all the time. Most won't kill completely dead tho. A lot will just give signal that will never fault a CEL. Bonus to changing the front O2 sensor, it will pay you back in fuel savings.

 

What do you mean by fault a CEL? Or fault completely dead? But the check engine light did come on, and that's what alerted me to get it checked out.

 

Rockauto.com for a new front sensor (denso upstream) 48$ shipped. Don't let a shop rape you for installing it. It takes a 22mm wrench or an o2 socket. And it's one one plug. Save yourself some money bro

 

I talked to the guy who sold it to me and his uncle owns a shop, so he's taking care of it for free. I'm still just worried that I bought myself a lemon.

 

think of the temperatures the front 02 has to endure, its quiet common to have them fail, 48 dollars is a cheap fix and if another code pops up and its not the o2 then you ll get that money back in fuel economy youll be saving, our cars tend to not trip the cel immeadiatly when the o2s starting to go, its got to die a complete painful death ( and expensive due to the fuel your pissing away ) to trip that code

 

I haven't driven the car enough yet (roughly only half a tank) to realize that I was getting terrible fuel economy. So are the rear 02 sensors the ones that indicate that the turbo, or something else more severe is failing when they break? From what I've read that seems to be the case, but I'm not sure.

 

the rear o2 sensor only monitors the catalytic converter to make sure it doing it job for emission purposes thats all

the front o2 sensor monitors and makes adjustments to the fuel trim to keep your car running efficiently. if your front o2 sensor goes bad your car will default to running super rich ( I E most likely why your getting bad fuel mileage)

the reason you may of got the system to lean code was the o2 sensor was on its way to going bad. if its dead your car should default to that rich mixture.

best bet is to get a new o2 sensor, reset the battery, see if you get the system to lean CEL again.

 

Depends on how agressive you drive will limit the life of the o2 sensor, reccomedation for an easy install, remove stock o2 housing and put a megan housing on and it makes it more accesible than stock. When i changed my o2 it got stuck in the housing so i just bought a new one to save time

 

True but. if the o2 is rusted in...most likely the o2 housing bolts are ruted in there too. and the stock o2 housing oe and o2 housing is a PITA to get off with out taking the entire turbo set up off

 

Well thanks for the help guys, I got just what I needed. Great community by the way. It'd be great if a mod could close the thread.

 

you can close it.

on the top of the thread go to thread tools, close thread

but its nice when you post about a problem or an issue, when you get it fixed to post what the fix was

 

02 sensors aren't hard to change, the front one requires a certain 02 sensor socket with a couple swivel head extensions, or a certain 02 sensor tool I've seen, unsure of the name, took 15 mins to remove use a bit of wd40 or pb blaster on the old sensor where it fastens into the 02 housing.....remove install new one with some anti seize on threads connect to connector, disconnect battery...relearn. your welcome.... I agree after changin myfront 02 I noticed a gas improvement. Good luck.

 

Well anyway it's all fixed now. It seems to no longer have any issues and I'm getting great gas mileage! Thanks for the help guys.

 

What brand sensor did you end up going with?


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