Diesel exhaust fluid is not used for regeneration, it is used to lower oxides of nitrogen emissions created by lean mixtures used to lower soot production during combustion. Diesel particulate filters catch exhaust soot to be reduced by regeneration. From Wikipedia, DPF filters go through a regeneration process which removes this soot and lowers the filter pressure. There are three types of regeneration: active, passive, and forced. Active regeneration happens while the vehicle is not in use and takes 10 minutes on average to complete. Passive regeneration takes place while driving using the heat of the exhaust. This works well for vehicles that drive longer distances with few stops compared to those that perform short trips with many starts and stops. If the filter develops too much pressure then the last type of regeneration must be used - a forced regeneration. This involves a garage using a computer program to run the car, initiating a regeneration of the DPF manually.
They also discuss "runaway" regeneration, where regen gets too hot, causing damage.
From a little research on DEF and DPFs, I haven't found a good reason for needing a manual regen, especially after A 1200 mile run at hiway speed, the DPF should have been clean.
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