the sensor when functioning properly reads 10k ohm ,so when sensor fails no longer reads the required resistance. Here is a great write up that doesnt require removing the tank and shows how to test which sensor is at fault. amazon has a 100 pack of the resistors for $6 with prime. im on my 3rd day with out a CEL. Good luck.

https://www.bimmerfest.com/forums/sh...=667126&page=8