Please help solve my puzzle!

[Billdozer2]

(07-29-2016 )Kenworth2012 Wrote:  The inlet should read higher than the outlet. The inlet reads raw exhaust nox. The outlet reads def treated exhaust nox. I changed mine about a month ago. Yes they were $450 each from Cummins and take in the old ones for cores. $70 core charge. Each. Yes CM2250. This was the forth time the sensors were replaced. The first three times they were supposedly replaced under warranty. They may have used knock offs or they didn't change them. So, after following Rawze, I'm doing the work and using the heck out of Cummins quick serve. Lots of info there.

What kind of numbers are you/were you getting with those NOx sensors through Insite?

My truck was regenning more than normal and the DPF pressure differential was up into the 5's. I removed the DPF and cleaned/baked it. The DPF pressure numbers are down under 1 now, but the truck is still regenning every 5 hours or so. I checked the NOx sensor readings and found that the inlet is around 150-200ppm at idle and the outlet is around 50ppm. I'm not really sure what the numbers are supposed to be, but it seems ok. I haven't checked what the numbers are when driving. I do have a check engine light for SPN 4364 FMI 18. Truck has 389,000 miles and the NOx sensors have never been replaced.

Is there any sort of test that can be performed on the sensors so that you know they are no good before replacing? I really dislike guessing. Especially when it involves almost $1,000.