Theory Of Operation
WARNING: This page is about a different car, the 2015 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) monitors the Diesel Exhaust Fluid (DEF) pressure buildup system to provide correct (overall) performance. If excessive air is detected during pressure buildup, the Purge Pump system draws fluid back into the DEF tank to remove the air. Once the purge is complete the pressure buildup is reinitialized.