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Possible temporary response to def head failure derate

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J&JD

RVF Supporter
Joined
Nov 3, 2019
Messages
2,283
Location
Fremont, California
RV Year
2017
RV Make
Newmar
RV Model
Dutch Star 4018
RV Length
40’
Chassis
Freightliner
Engine
Cummins ISL450
TOW/TOAD
Jeep Wrangler Sahara
Fulltimer
No
There have been many discussions on other forums concerning being stuck on the highway with a def head failure. If the def system fails the system will begin to derate the engine until the coach will become virtually immobile. This can, obviously, be potentially a very dangerous situation on a narrow busy road.
A temporary solution that might keep the coach running until you can get to a shop to have the codes/system checked is to disconnect the speedometer from the DS (left side) of the Allison transmission when def failure/warnings occur and before derate begins. Apparently this was recommended by truckers that have had the problem. I have no idea if this works. I’m just passing on the suggestion.

Here is a picture of the speedometer connection:
B7C7F0C7-BFC2-4D32-B568-AB0AB25ECDE6.png
 

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