[l8nit3]

Vehicle: E90 328i Xdrive 2011
Engine: N52
VIN: NN85977
KM: 165039
ISSUE: 0x2C7F - Bank2 sensor2 - lean trim
Diagnosis attempted: INPA values show B2S2 sensor voltage is erratic.
Fixes Attempted: Clearing codes, changing B2S2 o2 sensor

Back again with a nasty little gremlins of an issue.
Have just changed many parts within the last week:

-OFHG & mickey mouse flange
-Coolant drop
-Oil Change
-Both VANOS solenoids
-Both "non-return" check valves

Using "Bimmerlink" I've pulled a code 2C7F (Lean, not Rich), for Bank2 downstream sensor.
Using INPA I verified that the offending sensors voltage readings were indeed unstable. Then I changed that sensor.

I still have the same issue with fuel consuption, however the code hasn't re-appeared since last clearing.

Is it possible there is an air leak or the VANOS solenoids aren't seated correctly? Would that cause these type of errors?

Attached I'd the error report from Bimmerlink Ignore the DISA codes, I've done the x28i -> x30i upgrade and am awaiting my 3SIM.

Software available: All standard BMW tools + ISTA with bimmergeeks cable, Bimmerlink app, torque app, OBD Fusion app.

UPDATE:
So, after reseating the CAI intake boot, I had a few days of quiet, smooth driving.
Just last night on a routine drive around town, it began sounding like a de-catted tuner once again.

Could this be a loose 02 sensor? (Which I've changed)
Maybe a hole in the exhaust line between the cat and 02 sensor? (Non visible)
Possibly an exhaust manifold leak?

Any suggestions on where to start next would be greatly appreciated, I do not have access to a smoker or vacuum.

UPDATE #2:
I have narrowed it down to a likely exhaust manifold leak, in the rear manifold.

How do I possibly access it to do a soap test??
Any suggestions would be incredibly appreciated.
My current financial situation just took an incredibly unexpected turn, and I need to fix the vehicle ASAP.

[yfc500]

My 2006 330i E90 showed the same code 2C7F after ESL came on last month. I replaced all 4 O2 sensors. The car ran better for a few days. Now both ESL and 2C7F came back. I'm wondering if you have saved your issue. I would appreciate any suggestions.

[l8nit3]

Originally Posted by yfc500

My 2006 330i E90 showed the same code 2C7F after ESL came on last month. I replaced all 4 O2 sensors. The car ran better for a few days. Now both ESL and 2C7F came back. I'm wondering if you have saved your issue. I would appreciate any suggestions.

Yes, mine turned out to be a leak in the flange/gasket where the downpipes meet the rest of the exhaust system, just a few inches from the B2S2 O2 sensor.

This caused a false lean reading. Once the gasket was replaced, and seems welded, all was well and has been ever since.

[yfc500]

Originally Posted by l8nit3

Yes, mine turned out to be a leak in the flange/gasket where the downpipes meet the rest of the exhaust system, just a few inches from the B2S2 O2 sensor.

This caused a false lean reading. Once the gasket was replaced, and seems welded, all was well and has been ever since.

Thank you! Is it the one (red-circled in the attached) downstream from the sensors?

[l8nit3]

Yes that was exactly where my leak was. 150$ for welding and gaskets replacement , and good as new 👌👌

[yfc500]

Originally Posted by l8nit3

Yes that was exactly where my leak was. 150$ for welding and gaskets replacement , and good as new 👌👌

Thanks!