Selective Catalyst Reduction Nox efficiency low

[jrholder]

I have a Cummins ISL9 with a active SPN 4364 FMI 18 fault code. My local diesel shop did a forced regen and cleared the code but it was back within 25 miles. My nearest Cummins dealer is short staffed and could not give me an appointment (just let it sit in the yard and we will try to get to it). I am ready to make the 1400 mile trip from NY to Florida for the winter and find a shop there. Anyone drive with that code active that far? I saw a post that indicated it was a bad outlet Nox sensor and they had successfully installed a new sensor themselves. Not sure how they were sure it was the outlet sensor
and not the inlet sensor or something else. Someone else stated that theirs went into a de-rate mode but was drive-able vs a limp mode which I do not consider drive-able. I have driven quite a few miles with this fault code active and it runs just fine. This is a pre 2016 engine so not a DEF sensor issue.
Anyone else have experience getting this fault cleared?

[Ljwt330]

My understanding.

The forced regen cleaned out the DPF which could have tripped the code due to inadequate flow through the catalytic converter. The code returned because that was not the cause and it took a short trip to reset the sensors after being cleared. There is still a problem.

Can’t offer what it is beyond the two suggestions you gave. However, that NOx code will derate the engine and I believe will eventually go to limp mode as NOx reduction is the whole point of the SCR system. It is not a DEF sensor issue, but it is a critical DEF system issue if the computer thinks the NOx is out of spec.

[bigb56]

Don't know if it would work on the Cummins but in a pinch some guys on the Sprinter forum have successfully removed and cleaned NOX sensors. Others have successfully and temporarily removed and zip tied a NOX sensor to the frame, leaving it plugged in to keep it from going into the dreaded Mercedes "10 starts left" mode. It works like an O2 sensor so pulling it out of the exhaust stream lies to it