FMI 5 SPN 3361 / 2012 Cascadia...Need help diagnosing the problem / CEL MIL lights

Doubtful...did you get a DEF quality fault code? I don't see a correlation to open circuit fault code and "poor" quality DEF...

 

3364/2--Aftertreatment 1 Diesel Exhaust Fluid Tank 1 Quality Data Erratic, Intermittent Or Incorrect
3361/1--Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit Data Valid But Below Normal Operational Range - Most Severe Level

Basically you have a derate as per the spn 3361. You know...I wonder if you have a UQS on your truck. This would have been one of the very few in production that had a sensor in the DEF header. The truck should've got a recall to retrofit an analog header. Can you take a picture of the connector on your DEF header? I'll be able to easily tell what kind it is.

 

That's an analog DEF header....
So..in this case, a couple of things. You could have a lazy NOx outlet sensor. You could have bad temp sensors. At this point, you need Diagnostic Link and determine if your NOx conversion stays above 70% and your temps...and various other things that you need to monitor.

Something in your ATS is throwing off the calculation for perceived DEF quality. Maybe you have diesel in your DEF tank...or coolant. Not TOO big of a problem with this if you catch it soon enough and don't put off getting it fixed.

 

You'll just have to deal with the derate. You might be able to cycle the battery quick disconnect switch if you are equipped with one. But most likely you'll need DLink to clear the codes. And then verify what part is giving a faulty reading for poor quality.