...there is nothing in the DEF or Emissions related systems that will suddenly 'STOP' your engine - that is pure bunk. Cummins emissions related systems are not part of your ENGINE, only the emissions. The only related action is due to a low, or lack of, DEF liquid, which can send a signal to the engine to 'derate' it, meaning that it will govern your engine output to a lower mph speed, but has nothing to do with shutting it down or off.
The inherent reason behind any derate action is due to the government rules. They are striving to motivate drivers and owners to maintain the DEF liquid levels so that the system can properly take care of the emissions output. The derate is not to 'penalize' anyone, or cause an issue while on the road, or to limit them from getting to a place where they can add DEF, but only to give a firm warning that driving without DEF will not be allowed at typical highway speeds.
You could drive this lower speed all day long, if you wish.
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