4371 nox sensor after denox cat' plausibility

[Alliedacid]

X5d 2013 33k miles

So MIL lamp came on yesterday... code reader pulled this:

"4371 nox sensor after denox cat' plausibility"


2k miles ago the DEF Active tank was replaced for a bad internal ambient temperature sensor. (Warranty)..

Dropping it off today, Prefer to have some idea of the issue ahead of the bs the SA's tend to toss around.

Any thoughts?


Thanks

[Thecastle]

Originally Posted by Alliedacid

X5d 2013 33k miles

So MIL lamp came on yesterday... code reader pulled this:

"4371 nox sensor after denox cat' plausibility"


2k miles ago the DEF Active tank was replaced for a bad internal ambient temperature sensor. (Warranty)..

Dropping it off today, Prefer to have some idea of the issue ahead of the bs the SA's tend to toss around.

Any thoughts?


Thanks

Sensors pre and post scr meetering are probably bad. I've had to replace min as well about the same time the def tank died. Common failure. Read about it on e90post

[serge1]

Originally Posted by Alliedacid

"4371 nox sensor after denox cat' plausibility"

Any thoughts?


Thanks

As said before, there are 2 sensors that measure NOx.
Upstream (pre-SCR) takes initial measurement, downstream (post-SCR) takes after-treatment measurements.
If difference between 1st and 2nd sensor is less than 60 parts-per-million of NOx, the system begins to keep an eye and eventually logs a fault.

The assumption is then made that it is a faulty sensor, rather than inefficient SCR system that is the reason for lower difference in ppm values.

By the way, it has been said on the forums, and seems to hold some truth, that both sensors are basically a maintenance item, expected to last around 50K miles.
Both sensors in my 35d were replaced at 50K (warranty), then pre-SCR was replaced by me at 95K, and now i have fault stored for post-SCR at 109K miles. So, we have a trend here .

Dealer repair instructions state to replace both NoX sensor, even if only one is showing fault. Not a problem if under warranty.