P0156 / 2C78 error code won't go away

eurenn · 02-05-2024, 05:54 PM

I'm losing my mind over this issue. I've been getting the error code for the Bank 2 Sensor 2 (after catalytic convert) o2 sensor for ages. I've already replaced the sensor with a brand new one. But no matter what I've tried the error code will not go away. Each time I clear it, it just comes back on almost immediately after starting it back up.

My bimmerlink app shows me the 2C78 code, while my NT530 tells me it's P0156. I'm attached photos/screenshots of everything, just in case something might stand out to any of the experts who might be reading.

Also worth mentioning, occasionally on immediate startup, it will smell odd. Kind of like paint chemicals. Maybe related to the sensor giving bad readings to the computer?

2012 X5M, 137k miles.

jbash87 · 02-06-2024, 06:10 PM

P codes are useless for BMWs. Stick with Bimmerlink or better.

Not an S63 expert, so take what I say with a grain of salt. Hopefully an N63 expert can chime in.

Post cat O2 codes won't do anything but cause you to fail emissions testing if you have it. They don't change how the engine operate, they only tell you whether your cats are working or if your sensor is broken. So don't worry about anything negative happening to the engine.

What brand sensor are you using? I've heard that a lot of BMWs are very sensitive to brand and I believe that OE is Bosch.

tomjonesBT33 · 02-06-2024, 08:14 PM

Have you checked the downpipe where it bolts to the mid pipe section? If that’s loose or not sealed well, it’s possible that air could be mixing in and causing a bad reading. It could also cause a bad temperature reading too.

eurenn · 02-08-2024, 01:22 PM

Quote:

Originally Posted by jbash87

What brand sensor are you using? I've heard that a lot of BMWs are very sensitive to brand and I believe that OE is Bosch.

It's definitely not Bosch. It was a cheaper brand for sure. I went ahead and ordered the correct Bosch sensor today, once it's arrived and I've installed it I'll report back.

eurenn · 02-13-2024, 04:32 PM

Okay so I received the new o2 sensor below, and reset the error. It still came back on.
https://www.rmeuropean.com/Products/...125-MFG14.aspx

So now all I can think of to do is check the downpipes to see if anything is loose.

02-05-2024, 05:54 PM	#1
eurenn New Member 2 Rep 6 Posts Drives: 2012 BMW X5M Join Date: May 2023 Location: Des Moines, IA iTrader: (0)	P0156 / 2C78 error code won't go away I'm losing my mind over this issue. I've been getting the error code for the Bank 2 Sensor 2 (after catalytic convert) o2 sensor for ages. I've already replaced the sensor with a brand new one. But no matter what I've tried the error code will not go away. Each time I clear it, it just comes back on almost immediately after starting it back up. My bimmerlink app shows me the 2C78 code, while my NT530 tells me it's P0156. I'm attached photos/screenshots of everything, just in case something might stand out to any of the experts who might be reading. Also worth mentioning, occasionally on immediate startup, it will smell odd. Kind of like paint chemicals. Maybe related to the sensor giving bad readings to the computer? 2012 X5M, 137k miles. Attached Images
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02-06-2024, 06:10 PM	#2
jbash87 First Lieutenant 250 Rep 391 Posts Drives: 2006 M5, 2012 X5d, 2008 E91 Join Date: Aug 2012 Location: Seattle iTrader: (0) Garage List 2012 BMW X5 35d [10.00] 2006 BMW M5 [10.00]	P codes are useless for BMWs. Stick with Bimmerlink or better. Not an S63 expert, so take what I say with a grain of salt. Hopefully an N63 expert can chime in. Post cat O2 codes won't do anything but cause you to fail emissions testing if you have it. They don't change how the engine operate, they only tell you whether your cats are working or if your sensor is broken. So don't worry about anything negative happening to the engine. What brand sensor are you using? I've heard that a lot of BMWs are very sensitive to brand and I believe that OE is Bosch. Last edited by jbash87; 02-06-2024 at 06:17 PM..
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02-06-2024, 08:14 PM	#3
tomjonesBT33 Second Lieutenant 177 Rep 267 Posts Drives: 2006 Z4 M Roadster Join Date: Oct 2019 Location: VA iTrader: (0) Garage List 2012 BMW X5M [0.00] 2006 BMW Z4 M Roadster [0.00]	Have you checked the downpipe where it bolts to the mid pipe section? If that’s loose or not sealed well, it’s possible that air could be mixing in and causing a bad reading. It could also cause a bad temperature reading too. __________________ 2006 Z4 M Roadster - Silver Grey Metallic 2011 X3 xDrive28i - Deep Sea Blue Metallic 2012 X5 M - Monte Carlo Blue Metallic 2017 X1 xDrive28i - Alpine White
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02-13-2024, 04:32 PM	#5
eurenn New Member 2 Rep 6 Posts Drives: 2012 BMW X5M Join Date: May 2023 Location: Des Moines, IA iTrader: (0)	Okay so I received the new o2 sensor below, and reset the error. It still came back on. https://www.rmeuropean.com/Products/...125-MFG14.aspx So now all I can think of to do is check the downpipes to see if anything is loose.
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