[obiltagi3]

Hello everyone,

I've been experiencing rather unusual downstream O2 Sensor codes that won't go away. After countless hours of diagnosing and spending quite a bit of money i feel defeated and have finally decided to ask for some support from the community!
Just two quick notes: new O2 sensors, same codes, local shop verified O2 sensors were fine. Im aware of the Service Bulletin addressing some code fixes, current I-Level is below and newer than bulletin. I'm on BM3 currently, however, codes persist on stock flash. Any help would be much appreciated. Below is a list of parts changed and the codes im experiencing. Car drives excellent and just passed smog (I was able to catch it while the CEL was off). All monitors complete.


Replaced the downstream O2 sensors (upstream are new too)
Replaced both intake ducts
Replaced both MAF sensors
I Level is : F010-19-11-520
((2019) newer than than the bulletin)

Codes:
12AB04: Lambdasonde2 Bank1, electrical: Line break
12AC04: Lambdasonde2 Bank2, electrical: Line break
12B701: Heating Lambasonde2 bank1, function: internal resistance too high
12B801: Heating Lambasonde2 bank2, function: internal resistance too high

2015 N63TU 550i
BM3 STG1, XHP STG1, N63INTAKE OIL COOLER VALVE

I appreciate your help. Thanks

[ChiltiCoatl89]

Check those O2 Sensor connections very thoroughly. Something possibly with your Catted DP, however My educated guess its the connections itself.

[obiltagi3]

Originally Posted by ChiltiCoatl89

Check those O2 Sensor connections very thoroughly. Something possibly with your Catted DP, however My educated guess its the connections itself.

Oem downpipes were installed about 2 months ago. Codes continue (ignore my signature) ) A local shop said they were able to get readings from the sensors and that they were fine... Pins are in good condition and clean.
Tip: The O2 sensors im using are the OE Bosch 15167, not original BMW. I don't see that being an issue, just wanted to share. Thanks for the input!

[ChiltiCoatl89]

Only thing else I Could think of of they are installed in the wrong banks, I am not exactly familiar and stand corrected if they're the same PNs (Or not) as I am still learning BMWs, however Back to OEM Dp you shouldn't be throwing codes like that. Good post!

[obiltagi3]

Originally Posted by ChiltiCoatl89

Only thing else I Could think of of they are installed in the wrong banks, I am not exactly familiar and stand corrected if they're the same PNs (Or not) as I am still learning BMWs, however Back to OEM Dp you shouldn't be throwing codes like that. Good post!

Bank 1 & 2 use the Bosch 15167 for the downstream (monitor) O2 sensor.
Thanks for reaching out and I appreciate the feedback!

Anyone else have some thoughts to share? Thanks!

[obiltagi3]

Bump! Willing to give a small token of appreciation to anyone who provides me a solution that fixes this!

[ChiltiCoatl89]

Not gonna ever give up on helping a fellow 5er owner!

[ChiltiCoatl89]

Have you tried swapping the O2 sensors for new ones to make sure they are not the issue? Or one at a time? Always good to try that. For peace of mind?

[obiltagi3]

Yes I have just changed them again.
The codes continue, however, I think I have finally found the solution. Will keep updated.

[ChiltiCoatl89]

Originally Posted by obiltagi3

Yes I have just changed them again.
The codes continue, however, I think I have finally found the solution. Will keep updated.

Stay in touch!!! This will be another for the great Archives of the F10 Series forum.

[obiltagi3]

So, I decided to diagnose many of the AFR components. (You can see above the parts I changed)
Realized it’s been 35K miles on spark plugs, tuned and no misfires. Anywho, decided it was time to change plugs and coils. (I prefer to change these before a CEL, as I know the interval is coming up soon). Spark plugs looked pretty fouled. I’ve changed plugs on previous F10 over 10 years so I know how they typically look. For some reason, these plugs looked like they had some kind of buildup. I’ll post a pic for anyone who wants to chime in on what that buildup might be?

Anywho, I have not received any O2 downstream codes since the change of plugs + coils. All monitors are up (nothing changed here). No CEL. 120 miles in, will check back in a couple more hundred miles but all is looking good now. Looks like I needed spark plugs for a whole year despite car running fine and no misfires

I’ve never seen spark plugs cause O2 downstream sensors issues, can anyone explain this?

I hope this helps someone in the future! Thanks

[obiltagi3]

Here’s a pic of the plugs; as you can see, many of them just look burnt or like a typical used spark plug.
However, 4 plugs, that were in cylinders 3/4 and 7/8 had some kind of rusty looking buildup.

[ChiltiCoatl89]

I am looking into what may cause the discoloration, other than normal wear, Rich/lean differences in buildup.

[ChiltiCoatl89]

Running lean on your spark plugs, Grayish color which means plenty of air or more air to fuel, of course, and you are in OC in California? or?

[obiltagi3]

Originally Posted by ChiltiCoatl89

Running lean on your spark plugs, Grayish color which means plenty of air or more air to fuel, of course, and you are in OC in California? or?

Interesting, I was running the front mount intake for a while. It looks and sounds good, but went back stock when I saw how much dust was coming through the PG air filter into piping

[ChiltiCoatl89]

To me the corrosion or rust looking material, my educated guess, could be from trapped moisture before the seal of the electrode of the spark plug, from condensation. Doesn't look harmful as the seal did its job. Evidence of the car being in humid conditions. Has your car ever sat for long period of time without starting? Or is it parked outside?

[obiltagi3]

200 miles in no CEL


Car is always parked outside, it’s my daily driver ! The vehicle is home to California

Appreciate your help !

[ChiltiCoatl89]

Originally Posted by obiltagi3

200 miles in no CEL


Car is always parked outside, it’s my daily driver ! The vehicle is home to California

Appreciate your help !

Always!!! Happy Driving!! I go to So Cal every now and then, perhaps we all should do a Bimmers and Coffee meet somewhere lol

[obiltagi3]

Originally Posted by ChiltiCoatl89

Always!!! Happy Driving!! I go to So Cal every now and then, perhaps we all should do a Bimmers and Coffee meet somewhere lol

Sure! Just pm me if you’re in town