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P0031 but likely not the Front O2 sensor - Help!
P0031 but likely not the Front O2 sensor - Help!
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Old 04-13-19, 03:06 PM   #1
busyychild
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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!

Last edited by busyychild; 04-14-19 at 11:11 AM.
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Old Today, 03:33 AM   #2
Samurai Jack
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Default Re: P0031 but likely not the Front O2 sensor - Help!

You can definitely throw a P0031 CEL and not blow a fuse.

Sounds like your issue came from the frayed wire.
When you replace the O2 sensor just make sure you secure the sensor wires with some zip ties so they stay out of the way.
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Old Today, 03:44 AM   #3
busyychild
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Default Re: P0031 but likely not the Front O2 sensor - Help!

Quote:
Originally Posted by Samurai Jack View Post
You can definitely throw a P0031 CEL and not blow a fuse.

Sounds like your issue came from the frayed wire.
When you replace the O2 sensor just make sure you secure the sensor wires with some zip ties so they stay out of the way.
That’s the hope. I’m going to replace the downstream sensor today.

I’m just wondering if/how the downstream sensor triggered a P0031, the upstream sensor DTC.

Last edited by busyychild; Today at 04:45 AM.
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Old Today, 09:54 AM   #4
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Default Re: P0031 but likely not the Front O2 sensor - Help!

You have to remember that CEL codes do not give an exact answer / point to the exact problem.

CEL codes are to be used as guidance only as they point you to a general area of interest, and can have many possibilities within that area.
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