Code 3364 and 3521 came on my truck out the blue

I’m new to trucking. I had a similar DEF problem totally different truck but I hear def problems run similar in most cases. I spent over $3000 looking for the issue and found out that it was just the filter pad at the bottom of the tank had gone bad and was clogging the lines. Try checking under the truck if it’s possible where the DEF is injected sometimes you can take that apart and wash it with a bit of water if it’s crusted or clogged to clear it and can keep you going for a bit or until it gets clogged again.
If it persist you may want to drain the tank and see if there is any debris in the tank. I’ve heard from most mechanics that getting DEF from the pump isn’t good because you can sometimes pick up a lot of debris and transfer them to your tank. It’s better to buy the box knowing that what you’re pouring in is pure and clear.

 

From my experiences it's probably not a real problem but more than likely a bad harness or weakening connection that's fooling the ecm. It can still lead to engine management taking over but if the condition isn't active they can't diagnose the fault. I'd wait till it lights up again ( and I bet it will ) before you throw parts at it that are likely ok.

 

They'll be able to see the inactive codes but there's no path to diagnose the problem, code has to be active so they can follow the steps to find the right fix.

 

It’s a 2020, don’t you have a Warranty on it still ?

 

If the codes aren't active you can't get to the root of the problem and all you can do is throw parts. Don't shoot the messenger, I don't care what you do I'm just explaining if the lights aren't on you can't properly fix it.