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I read this on another site: Two separate:
Howie, very common on Freightliner products from the big trucks down to the Sprinters. The Def Header is the DEF tank sump, filter and potentiometer unit (for the gauge if equipped) (no pump, that sits on top of the tank). No recalls that I am aware of.
The biggest issue we see in the North East is if you fill the DEF tank in the winter and park it for an extended period of time (overnight), since DEF freezes, by poor tank design (Freightliner tanks) there is no room for the DEF to expand as it freezes and it cracks the plastic header within the tank. We have a policy at work DO NOT FILL THE DEF AT THE END OF THE DAY, FUEL TANKS ONLY. We change them by the dozens as a result of that and what we have become a custom to "routine failures for no reason".
When the engine cannot see the DEF tank level it will send the engine into derate (power reduction), I have had them just shut an engine off at highway speeds already also if it was damaged and shorted internally. The trucks have an "ENG FAULT OVRD" switch (that's how its labeled), you can press the button on the dash while cranking the engine and it will restart to limp it somewhere, I believe it will give you 4 hours at that point.
Tiffin had a problem with Def head sensors with their 2017-2018 models. The sensors were defective from their supplier. The sensors would give a false reading and cause a MIL light and then a derate of the engine. Most failed by 20,000 miles. Ours just failed at 19,000 miles. I changed out the head myself. Tiffin shipped me the new part over night. On ours, the whole tank had to be removed which was the hardest part of the repair. Had to drain 10 gallons of def first.
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