Galveston deep freeze and a 3216-20 fault code

[GCAT9110]

I pulled my 2015 37TS out of storage yesterday, its only been sitting a week. I had drained everything and put droplights in the wet bay anticipating some record lows. The low outside ambient was 14 Degrees and I bet the enclosed storage may have visited something <28? Anyway, on the run back to my shop I had the yellow engine light illuminate about 8 minutes into the drive, not the yellow check engine light. Obviously, indicting an emissions fault. Bluefire pulled up a 3216-20-Aftertreatment 1 intake NOx drifted high, this is the one just off the turbo. I did hammer it a tad leaving the storage facility. After recording the fault I cleared the code with the Bluefire software and the light and code have not returned but I have not put the coach back on the road yet. Anyone ever run across this 3216-20 fault. I don't think it has anything to do with the extreme cold and I hate just to pop a sensor on it. I will most likely plug in one of our laptops and look at NOx sensor activity and make the call after I look at the data.

[Grumpy]

Could be frozen DEF line, it will freeze around that 14 degree point.

[GCAT9110]

It was in the upper 50s when I picked up the coach. DEF fluid does freeze but once thawed it is still usable. Under operation the DEF heater will keep it from freezing. I should have tripped a DEF heater fault or other DEF code if it was DEF related. If the front sensor is correct NOx gasses drifted slightly high right out of the turbo and did so for just a moment. NOx Sensor #1 (intake) is upstream of Particle filter, dosing injector and the SCR. The down stream NOx never saw the anomaly. I could have been caused by the hard acceleration I gave it when leaving the storage lot and then lifting when approaching the intersection. NOx is normally a product of heat, going from WOT to a quick deacceleration can produce some high CO and NOx. Like I said we will plug into it later today and look at NOx sensor activity. It could be a dirty Nox sensor, the coach only has 15K on it and is well taken care off. I seldom ever let it idle and if I do I always use the throttle bump to 950-1000rpm.

[GCAT9110]

UPDATE: I replaced the offending knock sensor and after 75 miles of driving no further faults. BTW The NOx sensor runs about 425.00.