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View Poll Results: Which Front O2 do you prefer/recommend/use?
Bosch 2 10.00%
NGK/NTK 3 15.00%
Denso 13 65.00%
Subaru (Nippon/Denso) 6 30.00%
AC Delco 0 0%
Airtex 0 0%
Walker 0 0%
General/Universal (non/spliced) 0 0%
Multiple Choice Poll. Voters: 20. You may not vote on this poll

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Old 04-05-2012, 10:46 AM   #1
Timmy_M2000
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2003 WRX Sedan
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Hello, I'm Tim. 2003 Subaru WRX WRB Sedan, P0171/031 codes. Working the
P0171


Fuel trim malfunction (A/F too lean)

then threw-

P0031
Front oxygen (A/F) sensor heater circuit low input

P0171 Troubleshooting help thread-
http://forums.nasioc.com/forums/showthread.php?t=475620


Now that introductions are over, on to the meat and potatoes.

There are multiple question threads pertaining to the Front O2 Sensor Part Numbers.

I've had to do this and in the process, did some homework on prices, sensor types, quality, issues, etc.

As for Prices, they vary from seller to seller, the best i found was $123 @ Amazon.com. (BS15537, Bosch 4 wire, wideband)

Here are the PN's-(Compatible to 2002-2005 WRX) **Many sensors (AFR) for this vehicle are made by Denso or from Denso blue prints, despite manufacturer name, but that doesn't mean all sensors are created equal.**

Here's a list of sensor part numbers which can be used to successfully replace the front oxygen sensor on a 2001-2005 2.0L WRX:
ACDelco - 213-2843
Airtex - 5S4302
Bosch - 15537
Denso - 234-9011
NGK/NTK - 24659 (or 24642 for some '04/05 Sti's)
Subaru - 22641AA042
Walker - 250-54004

Here is a full directory of engine codes for all Model Year Subaru's with computers-
http://www.troublecodes.net/Subaru/ (All CEL's)

DO YOUR HOMEWORK. Find the right sensor for the right price. But know what you're getting.

There's no reason to spend $100 or $200 more than you have to.

Feel free to add info, but if you plan to say something negative, have nothing to contribute, or try to thread jack, PM me first, or just don't be a jerk.

I hope this helps!

Feel Free to share your experience with the sensors in the poll, as to which brand you prefer.
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Last edited by Timmy_M2000; 06-08-2012 at 09:29 PM.
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Old 04-05-2012, 11:55 AM   #2
van_dutch
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There is only 1 front O2 sensor you should be using and that is the Denso OE replacement (234-9011) (2 sensors if you include the Subaru one which is the same thing). These cars are known to be picky and can have issues with other ones..
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Old 04-05-2012, 04:49 PM   #3
Timmy_M2000
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Very true, I went with the Bosch since it was the best I found for the price, and its made by Denso as well (for our applications). Like I said before, not all sensors are created equal, so its imperative to do the research. This serves only as a guide to eliminate search time for DIY guys. That's also why I added the poll to see where people are at with the sensors they used and what kind of performance they've seen with them, to inform future purchasers of what to expect or anticipate.
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Old 04-05-2012, 04:55 PM   #4
Bacon117
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I like NTK, I get them for free.
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Old 04-05-2012, 05:24 PM   #5
WeldingHank
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I had a bosch once, and only once. I didn't get a CEL but my fuel trims were forever more than 5% off (tuned the car myself before replacing) and my fuel milage seemed to suffer slightly. Got a Denso unit, milage came back, and back to 3% +/- on my fuel trims.

I could even see a difference on my wideband. When cruising with an oem/denso unit it would only bounce back/forth between 14.9 and 15.1 (target 15.07) and with the bosch would bounch between 14.6-15.3!
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Old 04-07-2012, 10:55 PM   #6
Timmy_M2000
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Still open, let us know what you think, this is to help everyone. The more we contribute the more it helps!
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Old 04-19-2012, 11:22 PM   #7
Timmy_M2000
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Running a Bosch Wideband, no issues. Runs great.
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Old 04-20-2012, 11:43 AM   #8
Sharpjeff6
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I replaced my o2 sensor bank one and I've done more research than ever trying to figure out why my CEL wont clear and pops up with the same Code P0031 but i replaced it with direct OEM parts....

Confused
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Old 04-29-2012, 11:35 PM   #9
Timmy_M2000
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Quote:
Originally Posted by Sharpjeff6
I replaced my o2 sensor bank one and I've done more research than ever trying to figure out why my CEL wont clear and pops up with the same Code P0031 but i replaced it with direct OEM parts....

Confused
Have you checked the wiring? Perhaps its a bad plug or maybe a defective sensor? Is it the correct AFR sensor for the car, sometimes the front and rear o2 sensors can be mixed up by parts guys, not saying that's the case, but if you know someone who can run a voltage check, give that a whack and see what comes up. Or try returning the sensor to eliminate that as a possibility. 3rd, or 1st if you have the means or a friend who does, run some logs and talk to a tuner to see where the issue is taking place. That'd be a great way to figure it out without burning more money.
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Old 06-08-2012, 09:32 PM   #10
Timmy_M2000
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Update *** running the Bosch AFR sensor, tuned great and AFR's are spot on (tuned by a PROFESSIONAL tuner), car runs great. No issues with the sensor at all.
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Old 04-25-2013, 02:09 AM   #11
throttlehappy
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Quote:
Originally Posted by Sharpjeff6 View Post
I replaced my o2 sensor bank one and I've done more research than ever trying to figure out why my CEL wont clear and pops up with the same Code P0031 but i replaced it with direct OEM parts....

Confused

Check that the O2 Sensor Heater Circuit Fuse has not blown Know a few cars that had the heater circuit fuse blow and since it is near the ECU and not in the engine bay or interior fuse box, they do not realise there is a 3rd fuse box for the Front and Rear O2 sensors
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Old 05-02-2013, 03:40 PM   #12
adecan
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Quote:
Originally Posted by throttlehappy View Post
Check that the O2 Sensor Heater Circuit Fuse has not blown Know a few cars that had the heater circuit fuse blow and since it is near the ECU and not in the engine bay or interior fuse box, they do not realise there is a 3rd fuse box for the Front and Rear O2 sensors
Where exactly is this 3rd fuse box located? Iíve also tried almost everything but the p0031 code still on.
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Old 06-03-2013, 11:06 AM   #13
Telemachus
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I'm having the same issue. Replaced with Bosch unit, disconnected the battery to clear the code...CEL came back on and won't go off now. I've driven around 100 miles since replacing the sensor.

Am I missing something?
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Old 06-03-2013, 11:31 AM   #14
fastnoypi
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Quote:
Originally Posted by Telemachus View Post
I'm having the same issue. Replaced with Bosch unit, disconnected the battery to clear the code...CEL came back on and won't go off now. I've driven around 100 miles since replacing the sensor.

Am I missing something?
i still don't know why folks pick the Bosch unit, sure some will work, some won't.. IMO its a gamble putting on a Euro company part on a Japanese car, regardless of price its a big waste of time when you get the one that doesnt work right.
You can find and trust a Denso unit and it will work 99.9% of the time at installation since they are OEM Subaru suppliers.
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Old 06-03-2013, 12:21 PM   #15
Telemachus
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Quote:
Originally Posted by fastnoypi View Post
i still don't know why folks pick the Bosch unit, sure some will work, some won't.. IMO its a gamble putting on a Euro company part on a Japanese car, regardless of price its a big waste of time when you get the one that doesnt work right.
You can find and trust a Denso unit and it will work 99.9% of the time at installation since they are OEM Subaru suppliers.
I'm guessing because it's readily available at Auto zone..etc.

Can you find Denso units locally?

And, is the CEL supposed to turn off pretty quickly after the new unit goes in?
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Old 06-03-2013, 01:45 PM   #16
fastnoypi
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Quote:
Originally Posted by Telemachus View Post
I'm guessing because it's readily available at Auto zone..etc.

Can you find Denso units locally?

And, is the CEL supposed to turn off pretty quickly after the new unit goes in?
None except the local dealership have them locally to me, but all of them can get them 1-3 days out. Its worth the wait.
And yes, an O2 associated CEL will turn off instantly once the new unit goes in.
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