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Old 08-03-2005, 02:10 PM   #1
doghouse
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Default P0031 Front O2 Heater Low

I've got the P0031 Code right now and I suspect it's keeping me from passing emmissions. I've tried everything I can think of to solve this and haven't come up with anything. I've got 13.9V at the heater connector when I have my probe on engine ground. With the car running I have 9.7-->9.9V on the connector itself. It's an uncut factory harness but I did check continuity for the ground wire. As well, I checked the ground from D8&D9 which is supposed to ground the whole shibang. I even went so far as to cut the wire at the ecu and put a wire around the car directly to ground. Nothing. I've also tried three other O2 sensors, although I doubt this is the problem as it's a heater low and not a sensor not working.

Any suggestions? Thanks.

-Matt
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Old 08-03-2005, 02:48 PM   #2
AKGC8
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US WRX swap?

D8 and D9 aren't the grounds for the 02 sensor

Last edited by AKGC8; 08-03-2005 at 02:53 PM.
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Old 08-03-2005, 03:12 PM   #3
doghouse
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yeah, US swap. What are D8 and D9 then? The black with blue stripe that join roughly 6in from the ecu into one wire? Maybe I have the numbers wrong, I'll go check?

They aren't grounds for the O2 per say, If I read correctly they should ground the ECU whatever it's doing to the O2 sensor.

Thanks
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Old 08-03-2005, 03:24 PM   #4
doghouse
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I should be more thorough in my post. I'm just tearing my hair out. I have 6 codes in total. P0183-Fuel Temp Sensor (twice), P0463- Fuel Level Sensor, P0031-O2 Heat low, P1400- fuel tank pressure solenoid low, P0447-Evap Emission Control.

Is it possible that these are cascading and "ghosting" the O2 code?

Anyone have any values to fake the fuel tank stuff for now?

Thanks
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Old 08-03-2005, 03:52 PM   #5
Randoramma
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hmmm, that sounds very familiar to what I had when I finished my swap. I still have the 0463 code.. When you wired up the ECU, what set of pinnouts did you use to?

Randy
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Old 08-03-2005, 03:56 PM   #6
doghouse
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how did you get rid of the rest of the codes? Did you have the P0031? How did you get rid of it?

Thanks
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Old 08-03-2005, 04:01 PM   #7
Randoramma
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Well the pinnout I had used to determine where to place pins had several sensors backwards, so I had to get a real copy of the ECU pinnouts and repin those sensors. I wiped several of my codes when I did that, and P0031 was one of them. I dont have the diagram with me, but I bet its D8 and D9 which wiped that code for me. BUT that doesnt mean it will work for you, thats why I asked where you got your pinnouts from.

Randy

Oh, and before I had done this, I went throught the FSM diagnostic troubleshooting guide and everything was fine... weird.
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Old 08-04-2005, 07:48 AM   #8
doghouse
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Did you get a chance to check your pinout? I'm using a wiring diagram that I got from the Subaru technical site. I also have the procedure for checking out the code and both agree that the D8 and D9 are grounds. Anyway, I've checked nearly everything that I can think of here and could use any help.

Thanks.
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Old 08-08-2005, 11:40 AM   #9
doghouse
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So nobody has any insight on this? Nobody had a similar problem? I really don't know what to do at this point.
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Old 08-08-2005, 04:37 PM   #10
Randoramma
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sorry I keep forgeting to bring in my pinnouts to work (where I have i-net access. Will try tommorow.

Randy
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Old 08-09-2005, 08:59 AM   #11
doghouse
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Thanks for trying. Maybe today?

-Matt
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Old 08-11-2005, 10:05 AM   #12
doghouse
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Any chance you remembered today?

Thanks
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Old 11-11-2005, 08:50 AM   #13
turboK
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Doghouse-

Did you ever figure this out? I have the EXACT same problem and code. All wires in the circuit have continuity, and the sensor is good... Even checked out the ecu in a brand new car, and no code... Very weird...
thanks
karl
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Old 12-13-2007, 10:42 PM   #14
elsanto
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bump from the dead, did you guys ever figure this out? I've got the same issue on a 98 outback swap
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Old 09-01-2008, 06:41 PM   #15
tja1618
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second bump from the dead. I have been running my 03 WRX on a OTS cobb stage 2 map. It has worked flawlessly up until this week. The first strange thing is that when I tried to have my car inspected there were a few systems that were 'not ready', whatever that means.

Catalyst
Oxygen Sensor
Oxygen Sensor Heater

However, when the guy showed me this, the car wasn't throwing any codes or CELs. A number of miles later I was at WOT accelerating (nothing crazy, merging onto the highway) when a CEL was thrown. Immediately I checked the code: p0031 - HO2S Heater Sensor Circuit Low

I wasn't sure what to make of this, but the car seemed to be running fine. I had to drive the car before I can get it checked out thoroughly (since I am at school), but everything seemed normal until just now when I apparently hit fuel cut in 2nd gear at WOT around 4500 RPM. It was very unsettling to say the least (especially since I went to hell and back getting a center differential replaced).

Does anyone know what the cause of this is? My next course of action is to inspect the sensor however I can and try to check the wiring. The only mods I am running are a TBE, short ram intake, and a cobb stage 2 map.

Please help
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Old 09-01-2008, 06:45 PM   #16
elsanto
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^^ with a car that old I'd throw in a new o2 sensor, there isnt much elese that can go wrong with the circuit unless you are doing a swap as i was, which just totally screwed it up.

put a new o2 in, the CEL's may have been hidden by the AP, and thats why your CEL isnt turning on..

good luck
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Old 10-23-2008, 04:59 PM   #17
MUscooby
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I just threw a c0031 yesterday while driving, car still ran fine but i was going to check into fixes. I reset the ECU to see if it was a false signal, but the CEL came back immediately. Then i took the car for a brief spin and it was running like the ultimate turd: rough/inconsistent acceleration and, according to my AP, my max boost is 12.0.

what is the deal? why am i only hitting 12.0 when i am running an OTS cobb stage 1 map? Is it all b/c of the damned o2 sensor?
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Old 10-23-2008, 05:03 PM   #18
elsanto
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Quote:
Originally Posted by MUscooby View Post
Is it all b/c of the damned o2 sensor?
Yes, most likely.
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Old 10-24-2008, 10:57 AM   #19
MUscooby
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^^ Good idea/bad idea... going to my economy map (AP) until i get the new o2 sensor installed? Stock map?
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Old 10-24-2008, 12:24 PM   #20
elsanto
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I wouldnt recommend driving at all without a front o2, the car will run pig rich, and you really have no control over AFR...
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Old 10-24-2008, 01:07 PM   #21
MUscooby
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^^ yeah that's probably the best idea

should have the new o2 sensor in a couple days, then i just have to drive to my friend's place where i can install it. its gonna suck not being able to get around, though.
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