2C32 AND NOW 2C6C after replacing both pre-cat o2 sensors. Stumped.

elite. · 09-29-2018, 03:49 PM

Hi folks.....looking for some insight.

I use MHD with DPs and FMIC. I added the DPs this summer, and shortly after I got lambda control 2 (2C32). With 69k on the clock I decided to replace both pre-cat sensors because my mechanic was already in there.

Fast forward 100 miles and now I am getting both codes. 2C6C looks to be post cat sensors. Do you think replacing the post cat sensor on bank 2 would help? Some people say the post cats do NOTHING at all, while other posts say similar situations were resolved by replacing post cat(s).

The car idled rough before replacing the pre-cats, and after that it seemed to run ok. Once I did notice a little rough idle after replacement but since it seems to be running strong. I did try to reset adaptations but for some reason the MHD app wont do it, its giving me an error.

Anyway, any help would be appreciated.

mj6234 · 09-29-2018, 11:31 PM

23C2 was solved by a rear O2 for me. Not going to type it all out, but the DME compares readings between the two sensors. If it finds something it does expect you get the trimming codes.

elite. · 09-30-2018, 01:15 AM

So what your saying is the post cat is seninh something it doesn't like related to fuel trims and throwing that code(s) still....I think I'm in agreement, they have to be there for a reason. Leaning towards replacing bank 2 post cat.

mj6234 · 09-30-2018, 03:40 PM

Yes. I made a post on it at some point with my observations. There is an interaction between the two sensors.

tan_rich · 10-02-2018, 12:18 PM

Post cat o2 sensors affect your long term fuel trim. Over time your short term fuel trims will follow and you will get all sort weird fueling issues.

10-02-2018, 01:09 PM

It's not uncommon for post-cat O2 sensors to break or "go bad" when swapping DPs...swap in new ones and see what happens.

tan_rich · 10-02-2018, 01:24 PM

Quote:

Originally Posted by FCobra94

It's not uncommon for post-cat O2 sensors to break or "go bad" when swapping DPs...swap in new ones and see what happens.

I know that too well haha. Took my downpipes in and out about 4-5 times. Definitely would have been damaged through all that.

HawkeyeGeoff · 10-02-2018, 02:56 PM

If you have a "DPFix" in there as well, this effects the rear O2's. I had issues with my idle when I had one of those on there.

Sorry bro....looks like new rear O2's for you.

09-29-2018, 03:49 PM	#1
elite. First Lieutenant 37 Rep 348 Posts Drives: e93 Join Date: May 2013 Location: home iTrader: (2)	2C32 AND NOW 2C6C after replacing both pre-cat o2 sensors. Stumped. Hi folks.....looking for some insight. I use MHD with DPs and FMIC. I added the DPs this summer, and shortly after I got lambda control 2 (2C32). With 69k on the clock I decided to replace both pre-cat sensors because my mechanic was already in there. Fast forward 100 miles and now I am getting both codes. 2C6C looks to be post cat sensors. Do you think replacing the post cat sensor on bank 2 would help? Some people say the post cats do NOTHING at all, while other posts say similar situations were resolved by replacing post cat(s). The car idled rough before replacing the pre-cats, and after that it seemed to run ok. Once I did notice a little rough idle after replacement but since it seems to be running strong. I did try to reset adaptations but for some reason the MHD app wont do it, its giving me an error. Anyway, any help would be appreciated.
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09-29-2018, 11:31 PM	#2
mj6234 Private First Class 35 Rep 110 Posts Drives: E92 335i Join Date: Nov 2011 Location: US iTrader: (0)	23C2 was solved by a rear O2 for me. Not going to type it all out, but the DME compares readings between the two sensors. If it finds something it does expect you get the trimming codes.
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09-30-2018, 01:15 AM	#3
elite. First Lieutenant 37 Rep 348 Posts Drives: e93 Join Date: May 2013 Location: home iTrader: (2)	So what your saying is the post cat is seninh something it doesn't like related to fuel trims and throwing that code(s) still....I think I'm in agreement, they have to be there for a reason. Leaning towards replacing bank 2 post cat.
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09-30-2018, 03:40 PM	#4
mj6234 Private First Class 35 Rep 110 Posts Drives: E92 335i Join Date: Nov 2011 Location: US iTrader: (0)	Yes. I made a post on it at some point with my observations. There is an interaction between the two sensors.
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10-02-2018, 12:18 PM	#5
tan_rich Private First Class 21 Rep 165 Posts Drives: 2013 335is Join Date: Feb 2016 Location: OC iTrader: (0)	Post cat o2 sensors affect your long term fuel trim. Over time your short term fuel trims will follow and you will get all sort weird fueling issues.
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10-02-2018, 01:09 PM	#6
FCobra94 Guest 0 Rep n/a Posts Drives:	It's not uncommon for post-cat O2 sensors to break or "go bad" when swapping DPs...swap in new ones and see what happens.
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10-02-2018, 02:56 PM	#8
HawkeyeGeoff Captain 264 Rep 620 Posts Drives: E90 335XI MSport, S2000 Join Date: Dec 2016 Location: Waterford, MI iTrader: (1) Garage List 2011 BMW 335i XDrive [0.00] 2001 Honda S2000 [0.00]	If you have a "DPFix" in there as well, this effects the rear O2's. I had issues with my idle when I had one of those on there. Sorry bro....looks like new rear O2's for you.
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