Reductant Pump Assembly - Transit
The 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 the RDCM, which regulates system pressure by controlling pump speed using pulse width modulation (PWM).
When the RDCM requests reductant injection, the reductant injector opens and the pump operates, filling the reductant pressure line and injector and purging air from the system. When all air is purged, the injector closes and the pump builds pressure to 500 kPa (73 psi). The system is then primed and the injector provides diesel exhaust fluid (DEF) to the selective catalytic reduction (SCR) catalyst as commanded by the RDCM.
When the vehicle is shut down, the RDCM closes the injector and actuates the reductant purge valve, causing the pump to reverse flow and bleed down pressure on the reductant pressure line. The RDCM then opens the injector to allow gas to enter the reductant pressure line, which in turn allows the pump to purge all remaining DEF from the system and return it to the reductant tank. The RDCM closes the injector and returns the purge valve to the forward position.
The RDCM provides voltage to the reductant pump assembly internal heating element when the reductant temperature approaches -11°C (12°F).