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P0031 Causes

PostPosted: Wed Aug 02, 2017 10:24 am
by tkdbboy
Hey guys,

I have queried some of you on the facebook group and privately so thought I'd just put the info here in case someone runs into the same issue in the future.

So after having a new OEM front o2 sensor for 9 months, my car (PreFL 06 TBSTI) has started throwing P0031.
Since installing the new o2 sensor, nothing has changed to the car other than installing a new OEM MAF sensor in Feb.

Current observations:
- There is no pattern I can find to the throwing of the code.
Can happen twice a day or once every two days.
Can be before I start the car whilst it's cold to cruising after 30 minutes of driving.
No harsh vibrations seem to cause it which would help my suspicion of an electrical fault, but doesn't eliminate it either.
- AFR now tries to level at 13.8 rather than 14.7 (though very infrequently when idle it will try level out at 14.7)
- VVT logging at 1.5k neutral and cruising at 100kmph shows L & R were equal or varied by a maximum of 1
- Fuel consumption has gone from 11.8 to 13.0
- Fuel Correction @ 0.00 MAF g/s is up around 4%
- No rough idle as per 'common o2 sensor symptoms'

Possible causes that I've come across online (feel free to contest or add any):
- Bad o2 Sensor heater element (this should cause the code to be thrown constantly?)
- Bad o2 Sensor connection
- Connection issue with o2 sensor relay
- Blown fuse (SBF5 - Main relay fuse (also DLC, ECM, Fuel pump relay))
- Grounding issue
- Air leak?

My logs:
The most recent I have marked when the code gets thrown, WOT and weird AFR corrections to see if there's anything out of the ordinary with values during those events.
Compared to my old logs, does it look like my rear o2 sensor is behaving differently? Seems to be reading pretty low voltages consistently.

This is the point where AFR levels at 13.9 then 14.7: ... =7572-8076
If you zoom out, you'll see the same thing happening 7 times when I come to a stand still. I keep the car in D for most of them as I tried switching between N and D to see if it has an effect on it, but it doesn't.

My two most recent LVs:


Still trying to find the relay near the passenger side footwell.
It looks like PostFL and PreFL have them in different spots and the only other info I could find on it was USDM.
Are there any other electrical connections which would influence this code?

Extra info on the car:
- EJ207 Short Block
- Stock VF38
- AVO Dump & Mid
- Stock STI muffs
- Kobe 340lph Fuel pump
- Grimmspeed 3 port

Let me know if more info is needed to help eliminate possibilities.

Any thoughts and suggestions would be great.