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Old 04-17-2008, 09:55 AM   #1
HamrTym
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Default Front oxygen sensor life expectancy?

What is the general consensus on the life of the front (or lower) O2 sensor. I know it is a major contributor to the long term tuning of the engine via computer.

Will they definately throw a CEL when they are defective? Or do they lose their effectiveness over time gradually?

Got an '02 WRX wagon, with about 97,000 miles on it. About 65,000 of those have been at Cobb's Stage 2 map. Should I go ahead and replace it, or just wait until a CEL comes on as a sign?

Thanks for your time.

P.S. Sorry for any grammatical errors....
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Old 04-17-2008, 11:34 AM   #2
Jon [in CT]
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These sensors are designed to last a minimum of 100K miles. I wouldn't change a sensor until the ECU diagnoses a problem with it.
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Old 04-17-2008, 04:05 PM   #3
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^ yah, both of my cars WRX & Highlander had O2 sensor replace codes shortly after 100k miles. Don't worry, they will let you know when they need replacing. Is you gas milage starting to dip? Seemed to me when it got colder, that was when they started failing (increased resistance?).
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Old 04-19-2008, 12:51 AM   #4
txl146
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I replaced mine at around 80k, but it should last up to 100k miles easily.
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Old 04-19-2008, 12:59 AM   #5
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^ same
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Old 04-19-2008, 03:58 PM   #6
my scoop eats babies
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Mine crapped out around 90k, so ~100k sounds about right. It did in fact show signs of failing before the CEL came on, I dropped a few MPG before I got any CEL.
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Old 04-19-2008, 07:58 PM   #7
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agreed, just because you dont throw a code doesnt mean you might not have an issue. I remember Nissan use to recommend replacing them at 60k, but these aren't nissans obviously.
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Old 04-20-2008, 02:32 AM   #8
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My A/F sensor just went a month ago at about 110k.
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Old 04-22-2008, 09:30 AM   #9
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Had an mpg drop at about 85k and replaced it at 94k.
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Old 04-22-2008, 09:47 AM   #10
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...and did the mpg come all the way back up to where it had been upon replacement?
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Old 04-22-2008, 10:07 AM   #11
sinwagon
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No, but I have an issue finding the right O2 sensor. I've ordered 2 so far based on incomplete info on the web site.
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Old 04-22-2008, 10:13 AM   #12
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My A/F sensor died at 120k miles. I just want to know why a replacement costs $150. The dealership that does my alignments wanted $200... .
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Old 04-22-2008, 10:42 AM   #13
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Quote:
Originally Posted by jk988 View Post
My A/F sensor died at 120k miles. I just want to know why a replacement costs $150. The dealership that does my alignments wanted $200... .
Semi-wide band, 4 wire, pre-heated, and controls your Air/ Fuel (Sensor 1, Bank 1). Probably $50 bucks just to touch your car....
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Old 05-15-2008, 01:20 PM   #14
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my front o2 sensor just **** itself at 80k-ish.... no cel from it, just crappy gas mileage !!!!

yay, $200 dealer only part
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Old 05-15-2008, 03:59 PM   #15
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Quote:
Originally Posted by d1a9j View Post
my front o2 sensor just **** itself at 80k-ish.... no cel from it, just crappy gas mileage !!!!

yay, $200 dealer only part
If there isn't a sensor-related trouble code stored then it's very unlikely your crappy fuel economy is related to the operation of the front AFR sensor. And any auto parts store can sell you an exact replacement for your front AFR sensor, if it ever does malfunction.
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Old 05-15-2008, 04:46 PM   #16
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Quote:
Originally Posted by Jon [in CT] View Post
If there isn't a sensor-related trouble code stored then it's very unlikely your crappy fuel economy is related to the operation of the front AFR sensor. And any auto parts store can sell you an exact replacement for your front AFR sensor, if it ever does malfunction.
i went for a stage 2 street tune and the car was running super lean under boost (on stock tune) ... my guess is front o2 sensor is on its way out. also i cleaned my maf, so i dunno what else it would be
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Old 05-15-2008, 05:36 PM   #17
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Quote:
Originally Posted by d1a9j View Post
i went for a stage 2 street tune and the car was running super lean under boost (on stock tune) ... my guess is front o2 sensor is on its way out. also i cleaned my maf, so i dunno what else it would be
You damaged the MAF sensor trying to clean it. You introduced an exhaust leak downstream from the front AFR sensor while installing a stage 2 exhaust. You have an intercooler leak. The aftermarket wideband was mounted poorly in the muffler.

Any of these might be a reason you ran "super lean under boost."
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Old 05-15-2008, 06:38 PM   #18
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maf wasnt damaged, i had the problem before i cleaned it. no exhaust leak. not sure about the ic, but i doubt it. no wideband yet !

im honestly guessing its the o2 sensor
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Old 05-15-2008, 07:27 PM   #19
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Quote:
Originally Posted by d1a9j View Post
no wideband yet !
So, exactly how did you determine your engine was "running super lean under boost" without a wideband AFR meter?
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Old 05-15-2008, 08:45 PM   #20
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i dont have a wideband, but my tuner does... he hooked it up (innovate lc-1) and used his puter to get real time readings
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Old 05-15-2008, 09:02 PM   #21
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since 2000ish Subaru started usng a front Air/Fuel Ratio sensor before the cat. After the cats is where you will find Oxygen sensors.
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Old 05-15-2008, 09:12 PM   #22
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Quote:
Originally Posted by munkis View Post
since 2000ish Subaru started usng a front Air/Fuel Ratio sensor before the cat. After the cats is where you will find Oxygen sensors.
u know what i meant !!!
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Old 05-16-2008, 09:11 AM   #23
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Quote:
Originally Posted by Jon [in CT] View Post
So, exactly how did you determine your engine was "running super lean under boost" without a wideband AFR meter?
john im convinced its the 02 sensor on this car. this is the 2d one i had doing this. i pulled the af and cleaned it and it didnt make a change. the car has no boost or exhaust leaks wither. and its running afrs of 15 and 14 at wot on the stock map.i also suggested replacing the fuel filter
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Old 05-16-2008, 10:48 AM   #24
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Quote:
Originally Posted by Ray@revitup View Post
john im convinced its the 02 sensor on this car. ... and its running afrs of 15 and 14 at wot on the stock map.
The WRX's front A/F sensor is ignored during WOT. What was LTFT during these WOT runs? If the front A/F sensor is at fault for the lean WOT condition, then you should see a large negative value (e.g. -20%). The owner reports crappy fuel economy. If the front A/F sensor is at fault, then logging LTFT during idle and cruising should produce large positive values (e.g. +20%) and AFR logged by a wideband should be much less than 14.7 (e.g. 13.5).

I'm not a big fan of the shotgun approach to problem diagnosis (i.e. replacing every part in sight which MIGHT somehow be related to a problem).

Last edited by Jon [in CT]; 05-16-2008 at 10:56 AM.
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Old 05-16-2008, 10:59 AM   #25
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hey guys, if the front 02 sensors is bad would you have any funny idle issues??
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