Diesel mechanics, DEF isssue, need advice

I’ve got a 2015 Ram 3500 Diesel. 60k miles. Lately, I get this message: “Incorrect DEF detected. See dealership.” And the check engine light stays on.
Say what??? There is nothing wrong with the DEF. The only thing I can think of is that the truck isn’t being driven a whole lot right now. When I do drive it, I make sure it goes long enough to be fully warmed up - no shorty trips - and gets up to highway speed for at least a bit.

I’ve googled what I can find, which really isn’t much. It has not threatened to go into limp mode. I cleared the code on it once, 2-3 mos ago, now it’s back. Hubby goes hunting end of this month and that’s a really long trip with a lot of gear, and I sure don’t want the truck breaking down on him in the middle of nowhere.

The DEF is fresh, I only buy what we need, when we need it.


A couple things.

It should have given you a threat on limp mode (“150 miles to limp mode” or whatever).

Do you have the last jug or box the DEF came in? Can you check the date?

Also, filling the DEF tank 2 gallons or better triggers the diagnostic. 1 gallon or less not. If your husband is going on a trip, I would tell him to only add 1 gallon or less at a time until you get this ironed out.

I (luckily) don’t have DEF as mine is a 2012. I also don’t have any emissions anything on it anymore, but that’s besides the point.

Also, lots and lots and lots of reports of this issue.


Yes, I’ve been reading thru those forums.

No, it is NOT giving me a limp mode message. Don’t have the last jug anymore. We usually fill the tank when it gets down to about 1/2, so yes a large jug is 2.5g.

As for the emissions thing on yours… damn I wish…!!

My brother has a code reader. I’ll get him to plug it in and see what pops.

You can remove it. PM me if you want to know how. It’s not cheap. And, the answers are on those forums how to get it off…

Anywho, you can get a DEF checker on amazon. https://www.amazon.com/Refractometer-Measuring-Exhaust-Concentration-Engines/dp/B07DLDZBS8

That should tell you if this is an old jug of DEF or if the computer hiccuped.

The OBDII code reader won’t really get you further to an answer right now. Those are also dirt cheap on amazon, you should have one if you’re not going to delete the truck… :slight_smile:


I hope its not the same issue as my hubby had with his 2019 Ram. The DEF actually crystalized in the tank and he had to go to the dealership for them to empty and then flush out the tank. He added DEF like normal and it wasn’t reading on his gauge. It kept saying the tank was empty even though it was full. It also said it was going to go in limp mode so it took it to the dealership hoping it would be covered as he had extended warrantee. They of course would not cover it and it cost him almost $1000 to get it fixed.

They said it potentially froze (even though there is a heater in the tank!) and he added when it was 1/4 full. They stated it has to be filled before then (but how is one to know that!) and it froze and crystalized. So it had to be cleaned out and scraped.

Good lord. It’s summer time and this didn’t start until a few mos ago, so I would think freezing did not happen.
My fingers toes and everything else are crossed that they diagnose this CORRECTLY the first time and fix it. It’s going to be expensive no matter how ‘minor’ the problem actually is. I cannot afford to be nickel and dimed to death over it.

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For what it’s worth, everything I’ve read about this and limp mode the truck never actually went into limp mode.

That said, worrying about it on your DH’s hunting trip is not ok, so hopefully they get it corrected!

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