Time for a new pre-SCR nox sensor - DTC 4B6A
 

I'm guessing this is the 415mm pigtail one, number 11 below?

RealOEM.com - Online BMW Parts Catalog

My Rheingold test
https://youtu.be/ET6n2WR_vtA

My car is covered by the NOX sensor warranty extension, but the work can only be done by a US dealer, so I'd have to drive to Buffalo.

https://media4.giphy.com/media/WfyP9ebBuovu0/giphy.gif

$100 sensor from vehicle with 29k KM on its way from recycler.

I'd make the trip, they will likely end up replacing both NoX sensors.

first nox sensor looks healthy

second one seems to not oscillate as much.

could be the nox not sensing right or could be the cat is clogged up. or not sure if this is possible but would the urea injection fail open?

maybe the urea injection valve too.

basically anything after the first nox sensor could be bad.

did yo reset the nox adaptations on rheingold?