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Old 04-13-2019, 07:12 PM   #1
busyychild
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Member#: 270571
Join Date: Jan 2011
Chapter/Region: NESIC
Location: Somerville, MA
Vehicle:
2011 WRX
DGM

Default P0031 but likely not the Front O2 sensor - Help!

I have a 2011 WRX with 50k miles on it.

Recently threw a CEL, and checked it with my AP. I have a P0031.

Is it possible that a bad downstream (rear) o2 sensor could throw a P0031, and not blow a fuse?

Through troubleshooting I've noticed/discovered the following:

- Downstream (rear) o2 sensor wire has been frayed by driveshaft (possible short/have not tested)
- When downstream o2 sensor is unplugged from the wire-loom is does NOT throw a P0037
- When upstream o2 sensor is unplugged, there is no change (still have a P0031)
- There is no obvious damage to my upstream o2 sensor
- The 15amp o2 Heater fuse under the glovebox is not blown (I've swapped in known good fuses)
- I'm experiencing no change in engine operation (ex. not running rich, not bogging down, no surging)


I've reset the ECU each time (with my AP and unplugging the battery) performed a troubleshooting step (unplugging upstream/downstream o2 sensors) and driving around for a few miles.

I have a downstream o2 sensor on the way (DENSO 2344195 / 22690AA900). I will swap it in to replace the old one with the worn wire. I will do a better job of securing the wire this time. Hopefully that will remedy my CEL/P0031.

Any insight would help!
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Last edited by busyychild; 04-14-2019 at 03:11 PM.
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Old 04-13-2019, 09:12 PM   #2
Scorpius
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Member#: 370806
Join Date: Oct 2013
Location: Northern Indiana
Vehicle:
2019 WRX/STI DGM
2016 WRX/STI ISM

Default

I'd check your turbo inlet for tears. Might be letting unmetered air into the intake after the MAF.

My 09 wrx did this and I had a helluva time chasing my tail until I found the torn turbo inlet. If it's stock I'd inspect/replace anyways.
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Old 04-14-2019, 03:09 PM   #3
busyychild
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Member#: 270571
Join Date: Jan 2011
Chapter/Region: NESIC
Location: Somerville, MA
Vehicle:
2011 WRX
DGM

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Quote:
Originally Posted by Scorpius View Post
I'd check your turbo inlet for tears. Might be letting unmetered air into the intake after the MAF.

My 09 wrx did this and I had a helluva time chasing my tail until I found the torn turbo inlet. If it's stock I'd inspect/replace anyways.
Thanks! I'll give it a good look over.

In your case, do you know how the tear/unmetered air triggered a P0031 DTC? It seems unrelated.

Last edited by busyychild; 04-14-2019 at 06:18 PM.
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Old 04-14-2019, 09:20 PM   #4
Scorpius
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Member#: 370806
Join Date: Oct 2013
Location: Northern Indiana
Vehicle:
2019 WRX/STI DGM
2016 WRX/STI ISM

Default

Quote:
Originally Posted by busyychild View Post
Thanks! I'll give it a good look over.

In your case, do you know how the tear/unmetered air triggered a P0031 DTC? It seems unrelated.
It was two years ago and I don't know exactly what codes it threw. I was having issues with my a/f and idling issues AFAIK.

I had a cracked dp as well now that I think about it.

I apologize for not being any help.
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