2C31 Code after pre cat O2 sensor install

allcaps55 · 08-15-2018, 07:59 AM

Hello all,
Wondering if anyone has experienced something similar as I have not found many occurrences of this on other forums. My car is currently running MHD stage 1+. Mods are dp's, vrsf cat back exhaust, charge pipe with BOV, oil catch can and dci. I recently started getting the 2C31 pre cat SES code on my car so I went ahead and replaced those sensors. Both of them with the 17098 I believe. Car was running great after resetting adaptations although about 500 likes after I started noticing a rich fuel smell. Well today driving to work the 2C31 code reappeared. I'm wondering if maybe this is a sign that I need to replace the post cat O2's also as I've read that they are responsible for calibrating the pre cats? I just don't want to go throwing money at something that might not be the route cause. I have the shadow codes for having DP's installed so I cannot really tell if they are bad or not. Car has 91,000 and post cat O2's are original. If anyone has any suggestions please let me know! Thanks.

tan_rich · 08-15-2018, 09:25 AM

Issue is most likely stemming from the post cat o2's. If you take a look at your logs or gauges while driving check for your LTFT. I bet they are pegging high, 25% or higher which is triggering the 2c31. You'll notice less mpg and running richer smell.

Also if you have downpipes, you can run the stage 2/2+ tunes. Just make sure to uncheck or box or OEM/catted downpipes. Also to log it and check if everything is running good.

allcaps55 · 08-15-2018, 11:39 AM

Quote:

Originally Posted by tan_rich

Issue is most likely stemming from the post cat o2's. If you take a look at your logs or gauges while driving check for your LTFT. I bet they are pegging high, 25% or higher which is triggering the 2c31. You'll notice less mpg and running richer smell.

Also if you have downpipes, you can run the stage 2/2+ tunes. Just make sure to uncheck or box or OEM/catted downpipes. Also to log it and check if everything is running good.

Thanks for the info I have not had time to run logs but after asking around it seems like the post cat O2's are most likely the issue. I'm waiting to run stage 2 right now until my intercooler gets here at end of September

08-15-2018, 07:59 AM	#1
allcaps55 Private 13 Rep 83 Posts Drives: 2009 335i Coupe Join Date: Jun 2017 Location: Denver, CO iTrader: (0) Garage List 2009 335i [0.00]	2C31 Code after pre cat O2 sensor install Hello all, Wondering if anyone has experienced something similar as I have not found many occurrences of this on other forums. My car is currently running MHD stage 1+. Mods are dp's, vrsf cat back exhaust, charge pipe with BOV, oil catch can and dci. I recently started getting the 2C31 pre cat SES code on my car so I went ahead and replaced those sensors. Both of them with the 17098 I believe. Car was running great after resetting adaptations although about 500 likes after I started noticing a rich fuel smell. Well today driving to work the 2C31 code reappeared. I'm wondering if maybe this is a sign that I need to replace the post cat O2's also as I've read that they are responsible for calibrating the pre cats? I just don't want to go throwing money at something that might not be the route cause. I have the shadow codes for having DP's installed so I cannot really tell if they are bad or not. Car has 91,000 and post cat O2's are original. If anyone has any suggestions please let me know! Thanks.
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08-15-2018, 09:25 AM	#2
tan_rich Private First Class 21 Rep 165 Posts Drives: 2013 335is Join Date: Feb 2016 Location: OC iTrader: (0)	Issue is most likely stemming from the post cat o2's. If you take a look at your logs or gauges while driving check for your LTFT. I bet they are pegging high, 25% or higher which is triggering the 2c31. You'll notice less mpg and running richer smell. Also if you have downpipes, you can run the stage 2/2+ tunes. Just make sure to uncheck or box or OEM/catted downpipes. Also to log it and check if everything is running good.
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