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Old 04-22-2007, 03:51 PM   #1
warnockm
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Default Troubleshooting an oxygen sensor problem

I have a 2002 WRX and i just got a P0031 error: Heated Oxygen sensor voltage low. Theres a lot of discussion about this problem on the forums, so i'm going to follow the previous advise and check out the wiring first.

I ran into my first problem. Exactly where is the front oxygen sensor located!? I'm looking around the exhaust as it leaves the engine. I'm looking on the passenger side, and I've removed the airbox to get a better view, but i can't see anything w/ a wire coming out.
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Old 04-22-2007, 05:37 PM   #2
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If you remove the passenger side wheel you will see a (approximate) 1/4 circle panel in the fender well held in by 4 plastic pops. Remove that and you will get access to the oxygen sensor. It is about 4" before the start of the uppipe. You can also follow the wiring down to the sensor. The wire clips onto a bracket that shares a bolt with the passenger side rear coil pack.
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Old 04-22-2007, 06:48 PM   #3
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thanks. I found it just fine. All of the wiring appears in tact so i'll keep testing things.

BTW, i found this bracket literally lying on a piece of metal near the wheel. I don't think its related to this problem, but i have no idea what it is:



thoughts?
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Old 04-22-2007, 11:20 PM   #4
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I've got one of those in my parts-left-over-after-mods box. No idea where it goes. So far, the car is holding together, so I'm not too worried.
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Old 04-22-2007, 11:21 PM   #5
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Is it plugged in? I just did an uppipe swap and somehow ended up not plugging the thing back in.
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Old 04-22-2007, 11:26 PM   #6
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Quote:
Originally Posted by Feign View Post
Is it plugged in? I just did an uppipe swap and somehow ended up not plugging the thing back in.
Yes, i did check the connections at the sensor and at the connector by the airbox and they seem fine.

Theres 4 wires. The black should have power, 14V, but how can i check the readings on the sensor? is there a voltage or impedance range i should be aiming for?

Last edited by warnockm; 04-23-2007 at 12:59 AM.
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Old 04-23-2007, 01:28 AM   #7
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IIRC the sensor data is not voltage but variable current (amperage) so measuring it will require some trickery or cutting a wire in half. Best thing might be to borrow one from a buddy that is known good and swap it in.
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Old 04-23-2007, 01:48 AM   #8
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PM'ed relevant FSM pages.
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Old 04-23-2007, 08:30 AM   #9
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How many miles do you have? My factory sensor died at about 70k miles and it's been working great since I replaced it.
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Old 04-23-2007, 11:50 AM   #10
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Quote:
Originally Posted by turd_ferguson View Post
How many miles do you have? My factory sensor died at about 70k miles and it's been working great since I replaced it.
Just turned over 70k this month! I suspect it is the sensor but wanted to check the wiring just in case.
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Old 04-23-2007, 12:07 PM   #11
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Quote:
Originally Posted by warnockm View Post
Just turned over 70k this month! I suspect it is the sensor but wanted to check the wiring just in case.
Just a heads up when you replace it. The front "02" sensor is called a A/F ratio sensor. Good luck.
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Old 04-23-2007, 12:51 PM   #12
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http://www.wrxfanatics.com/lofiversi...hp/t21059.html

Did you check the entire length of the wires? Also, there's a small bracket that the thing is wiretied twice to. If you pull off that little plastic piece that gives access to the sensor and look up with a flashlight, you should be able to see where it's attached. Make sure it's attached to at least one of those points.
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Old 04-23-2007, 02:49 PM   #13
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There is a heating element in the O2 sensor, most likely the problem is with the senosr, the voltage low code, would happen if you have a short in the wiring, or sensor heating element. if you are getting battery voltage at the O2 plug, tap into the harness and check with the sensor plugged in, the heating element is like a filement in a light bulb, and will burn out over time, you can ohm test the sensor although I do not know what the readings are suppost to be.
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Old 04-29-2007, 10:24 PM   #14
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I just hooked up the OBD-II connector and checked the codes and got two codes: P0102 & P0113, along w/ the previous P0031. i cleared the codes and only the P0031 came back. P0102 Mass Air Flow (MAF) Circuit Low Input and P0113 Intake Air Temp Circuit High Input. Not sure if these are related.

Also, where's a good place to buy oxygen sensors for subarus?

Thanks,

Last edited by warnockm; 04-29-2007 at 11:39 PM.
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Old 04-29-2007, 10:52 PM   #15
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Well the temp gauge and MAF are housed in the same unit. You probably got those codes if you ever turned the key on with the MAF disconnected.
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Old 05-01-2007, 08:41 AM   #16
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Along w/ where to buy, what kind do you recommend? searching the forums i found some talk about Bosch sensors, but didn't see where to purchase them. I also need to pick up an o2 sensor socket.
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Old 05-01-2007, 05:35 PM   #17
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I just ran into the same issue and was searching online for 02 sensors. Densos seem to run a bit more than the Bosch and the cheapest I could find was $149. However that place was all out and wasn't expecting any more for a week or so, so I ordered one form Advanced Auto Parts for $168 shipped. If you look you can probably find one for cheaper. Just make sure it is a pre catalyst or front sensor. The rear sensors are much cheaper.
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Old 05-01-2007, 08:44 PM   #18
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Quote:
Originally Posted by Mr.Sparkle View Post
I just ran into the same issue and was searching online for 02 sensors. Densos seem to run a bit more than the Bosch and the cheapest I could find was $149. However that place was all out and wasn't expecting any more for a week or so, so I ordered one form Advanced Auto Parts for $168 shipped. If you look you can probably find one for cheaper. Just make sure it is a pre catalyst or front sensor. The rear sensors are much cheaper.
Cool thanks, i found them. I'll take it they are "upstream" sensors. Upstream from the Cat?
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Old 05-08-2007, 05:45 PM   #19
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Got my new sensor today and i have another question. The socket needed looks like a spark plug socket, but will not fit because of the wire. When i emailed partsamerica to ask about hte socket, they said to use a spark plug socket.

Does the 2ft wire remove from the oxygen sensor? I know oxygen sensor sockets are split. Was the tech support from parts america wrong?

thanks,
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Old 05-08-2007, 10:11 PM   #20
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Quote:
Originally Posted by warnockm View Post
Does the 2ft wire remove from the oxygen sensor? I know oxygen sensor sockets are split. Was the tech support from parts america wrong?
I just use a 22mm wrench. It works fine if you are careful.
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Old 05-08-2007, 10:29 PM   #21
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Harbor Freight and other places sell a specific O2 sensor socket, 22m with a cutout for the wire. Shouldn't cost too much.
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Old 05-09-2007, 12:09 AM   #22
warnockm
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Finally got the thing replaced. Thanks everyone! The bosch sensor changed beautifully and the wire casing seems a little better than the OEM. I reset the code and checked the Oxygen sensor outputs from both sensors. The dealership wanted $350 parts and labor to do this, and i got the parts from partsamerica/advance auto for $179. not bad! thanks again.
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Old 05-09-2007, 03:35 AM   #23
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Since the front sensor is actually an a/f ratio sensor, could it be replaced by
the vw wideband sensor from Turboxs?
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Old 05-09-2007, 10:17 AM   #24
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Quote:
Originally Posted by warnockm View Post
The bosch sensor changed beautifully and the wire casing seems a little better than the OEM.
If you had inspected the sensor body closely, you would have found that your 'Bosch' sensor was actually made by Denso, which also makes the OEM sensor.
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Old 05-09-2007, 02:16 PM   #25
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Quote:
Originally Posted by calib17a View Post
Since the front sensor is actually an a/f ratio sensor, could it be replaced by
the vw wideband sensor from Turboxs?
No, it's a completly dif. type of wideband.
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