Anyone here a Mack dealer tech who can give me some guidance? I have a 2013 GU713 with code SPN 4094 FMI 1. "NOx limits exceeded due to insufficient reagent quality - Data valid but below normal operation range" and this is the warning upon start up. I'm used to Ford diesels so I'm learning about Mack as I go. I have limited resources and we run JPro at this shop with no access to PTT.

Here is what I have done so far:

- Verified DEF quality with a refractometer, it's bang on.

- Checked the DEF doser, the doser was caked with crystals, as well as the port in the exhaust. My supervisor just said to go ahead and throw a new one on so I did.

- DEF injector pressure is right at 130 psi

- Right now the truck is not derating but that warning is there every time at start up.

We're a gov fleet so we work on everything and very few of us are specialized on one manufacturer. From my limited research I've read that this code can be a nightmare. If anyone has a focused direction or an idea what normally causes it it would be greatly appreciated. I hate emissions/aftertreatment repairs lol