Could be the NOx sensor again, if it were due to unrelated work then it would be a different code due to no communication with the sensor. The DPF and regens have nothing to do with the DEF/SCR system.

I would start by using an OBD-II scantool or adapter to read the NOx sensor readings to see if one of the sensors is being erratic.

Did you use a GM replacement sensor or aftermarket? Also, which NOx sensor did you replace? If you replaced the downstream sensor then that's not the same sensor that triggers the P20EE, that code comes from the sensor before the SCR.

 

Thanks everybody!

I replaced the upstream sensor with a AC Delco sensor.

Drove truck today, drives fine. After 100 miles, the Poor Quality DEF Message came up with the 100 mile countdown.

Checked codes again, now it is P249D and P20EE.

I hooked up OBD and saw 0 voltage on either O2 Sensor 1 and O2 Sensor on the OBDLink app. Is this what I am looking for? Or somewhere else in the app to see specifically NOx?

Thanks!

 

I wonder at what point the engine not running right from being plugged up with EGR stuff starts manifesting in odd issues like this? i.e. is it worth the cash at some point to clean out the intake side, walnut blast the ports, etc..

 

Just had this code happen a week ago. Took to my regular place; they looked at it and said "code is sort of generic, let's eliminate the obvious". They load tested the battery; was not holding 12V. Replaced battery; problem solved. Don't overlook the obvious

 

Great tip! Battery is fresh within last 4 months.

 

But definitely follow DieselDrax instructions - I had NOX downstream fail; it was clearly visible on a 'live' OBD2 scan output; it was jumping around like crazy but the first one was clearly in the range.

 

Isnt that one the upstream one? sounds like you replaced the downstream first time, now the upstream is out...?

 

You're correct, P20EE is upstream, P11DB is downstream. Fixed my post.