Warning: the 25 percent DEF warning light is not telling you what the book says

Mia Moore · 2026-10-17T19:15:03.878867+00:00

I got a 2019 Pete in last Tuesday with the 25 percent DEF light on and the driver swore the manual said he had plenty of time, since it's not the 5 percent one yet. Turns out on that year the 25 percent countdown can start derating way sooner than folks think, and the truck was already limited to 55 mph by the time he rolled in. Where do you all point customers to read up on the real countdown before they end up limping in on a Friday afternoon?

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Warning: the 25 percent DEF warning light is not telling you what the book says | Diesel Mechanics - Librear