Def light and error code p204f

Sorry if answer has already been addressed. I couldn't find a previous post about it.

I have a 2014 v4. I live in Idaho at 6300 ft. Today's temp was 40-50 degrees. At 6500 miles my def light came on. I filled the tank and the light went off. Yesterday at 9,400 miles it came on again. This time I bought 2, 1 gallon containers and put them both in. The light turned off.
This morning, about 50 miles later, I was driving up a mountain pass 8000 ft. Just before the top the def light and engine light both came on. Scan gauge has code p204f which looks to be related to def fluid.

Thoughts? Curious if Maybe I needed to add a little more def fluid? I cleared the code at gas station. Opened hood and removed def cap and put back on. On start up both cel and def light came back on.

Thanks for any ideas you can provide. I'm about 5 hours from nearest dealership.

I added another gallon. Both check engine light and def light stayed on. On my trip home again almost on the crest of the pass another light flashed! The dreaded 10x more starts left. Yikes. I called my closest dealer (5 hrs away). They said might be a bad sensor and that i need to bring it in. Any thought to save me such a long round trip drive would be awesome. Is it possible the DEF fluid is bad? Thanks.

Seems like lots of people on this forum have reported having similar symptoms and then having those sensors replaced, and it seems it doesn't always work the first time either.

Just search for def tank sensor

T'were me, I might go for a good long drive several times around the dealership before you take it all the way back home again after they think they're finished.

My 2014 had a bad NOX sensor and it took several trips to get it diagnosed and changed. Would give the warning for only 5 starts till engine shutdown with DEF tank full. No more warnings after it was changed.


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Larry (I think that is your still name?)

Def fluid has an unpublished and unidentified shelf life; so it should be purchased were its stock is quickly turned over. Mine went off during winter storage and the Def light problem was solved by draining the Def tank and completly flushing it prior to refilling with "new stock" fluid. Hope this helps?

MB ended up towing my van 350 miles to the nearest dealer. Turns out it was a bad nox sensor. The dealer replaced it and I drove it back home, no DEF or CEL lights, life is good.

DEF has a shelf life and it varies by climate.

Q. What is the shelf life of DEF?
A. The shelf life of DEF is a function of ambient storage temperature. DEF will degrade over time depending on temperature and exposure to sun light. Expectations for shelf life as defined by ISO Spec 22241-3 are the minimum expectations for shelf life when stored at constant temperatures. If stored between 10 and 90 deg F, shelf life will easily be one year. If the maximum temperature does not exceed approximately 75 deg F for an extended period of time, the shelf life will be two years.

http://www.cumminsfiltration.com/pdfs/product_lit/americas_brochures/MB10033.pdf