[Carl n Susan]

Well Frank, reading the manual won't tell you much. Here is the *COMPLETE* description of the Diesel Exhaust Brake switch from page 37 of the Ford 2015 DIESEL Supplement.


GENERAL INFORMATION
Diesel Engine Braking
This feature increases engine braking at higher engine speeds to provide better grade descent control with less brake and transmission wear and tear.

Press the button located on the switch bank next to the audio unit to switch the system on or off. A light will illuminate in the instrument cluster when this feature is switched on. You can use this feature with tow/haul to provide further increased engine braking. For more information on tow/haul, see Automatic Transmission operation in your Owner's Manual.

Isn't that the most informative thing you have ever read? Maybe the Ford 2015 SUPER DUTY Owner’s Manual explains more under Automatic Transmission operation? Nope, there is no mention of the Diesel Exhaust Brake in that section or even the entire manual.

It would be interesting to know the difference between Tow/Haul and the Diesel Exhaust Brake. But Ford doesn't seem to think it is important enough to document. Maybe someone will ask the real experts on one of the Ford truck enthusiasts discussion forums.