P208a DescriptionThe reductant pump assembly contains a diaphragm pressure pump, a pressure sensor, a purge valve, an outlet filter and an internal heating element. The reductant pressure sensor provides feedback to Powertrain Control Module (PCM), which regulates system pressure by controlling pump speed using pulse width modulation. When PCM requests reductant injection, the reductant injector opens and the pump operates, filling reductant pressure line and injector and purging air from the system. When all air is purged, injector closes and pump builds pressure to 73 psi. (500 kPa). The system is then primed and injector provides DEF to the SCR catalyst as determined by PCM.
When the vehicle is shut down, PCM closes injector and actuates reductant purge valve, causing the pump to reverse flow and bleed down pressure on reductant pressure line. The PCM then opens injector to allow gas to enter reductant pressure line, which in turn allows the pump to purge all remaining DEF from the system and return it to reductant tank. The PCM closes injector and returns purge valve to forward position. The PCM commands glow plug control module to provide voltage to reductant pump assembly internal heating element when reductant temperature approaches 12°F (-11°C).
P208A Information for specific makes
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