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Need help finding Front (Upstream) O2 (A/F) Sensor

16K views 14 replies 4 participants last post by  irickchad 
#1 ·
2011 WRX Prem. This sensor was fine, but since placing it back into the collector after replacing my stock up-pipe, my car throws code P1153 after a half hour or so of driving. It's listed as an O2 sensor by some sites, and air/fuel on others, but I know it's the one the accessport reads air/fuel with. It seems to run, idle, etc, just fine, but then will suddenly peg to 20.8 AFR and throw a code, especially while cruising on the interstate. I found it for $109 on Amazon, and $103 on RockAuto, just wanted to see if anyone can find any better deals, or if anyone has had any experience with this issue and has fixed it without sensor replacement.

Here's a link to the one I found on amazon, it's Denso PN 234-9108 I think it's the right one, definitely trying to double check before I order a new one. Amazon.com: Denso 234-9108 Air Fuel Sensor: Automotive
 
#3 ·
Bank 1 Sensor 1. I haven't removed the harness and the whole thing is heat wrapped, so I'm not sure. It's whatever's stock for the '11.

I keep getting annoyed because I find PN's that say they're for upstream and they're for downstream, etc. Shouldn't be this hard just to find the correct sensor, lol.
 
#6 ·
There is only two. One at the very end of the header, and one after the cat in the downpipe.

Typically, when someone installs an aftermarket DP they will have a bung welded in before the cat in the downpipe for a wideband O2 gauge. That's the only time there should be three. And the wideband will have no influence on the operation of the car. It's strictly for gauge use and sometimes data logging.

Sent from a long time ago, in a galaxy far, far away
 
#9 ·
I called Denso to figure this one out. It is indeed replacement part # 234 9108 thru denso if anyone reads this in the future. Hopefully it gets rid of my code.
 
#11 ·
Idk if I dinged it against the threads too hard while I was installing it, or if the wiring was just brittle after all that time so close to the heat that an uninstall/reinstall messed it up, but it's definitely on the fritz.
 
#13 ·
Yeah, now im just hoping it fixes it. Seems to be super common replacement part for the forester guys, from what ive researched... just not so much for us.
 
#14 ·
I've come across a few people having to replace it right around 100k. I did mine at about 110 but it set off around 108 109

A few people were earlier. I've actually seen a brand new 2015 volvo xc60 need one replaced...some crazy things happen

I can see that if the wire was frayed a bit, that can cause intermittent power or signal
 
#15 ·
Like I said, it's really weird. It has varying voltage (via accessport) and at times, measures just fine, then out of nowhere it's at 20.8~ again, and stays there til it decides to start metering correctly again.
 
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