Note: Air supply must remain active while the system purges.
Under certain conditions the aftertreatment control system will run the DEF dosing system through a DEF purging cycle. This purge cycle will drain the DEF line between the dosing cabinet and the DEF injector. The purge cycle is designed to protect the DEF system, and to prevent the DEF from freezing. The purge cycle also protects engine exhaust hardware from DEF leaking from the DEF injector. The system will enter purge mode when the engine speed has dropped below a set threshold. The system will also enter a purge cycle if certain codes are logged during operation.
During purge cycle, the DEF return valve on the DEF manifold will open and the dosing pump is turned off. The purge cycle will allow the air pressure in the line to force remaining DEF in the nozzle/line back to the tank inside the dosing cabinet. The purge cycle is a time-based event. The event should take less than 1 minute.
Dosing air supply must remain pressurized with air available always during engine operation. This is required to ensure that the urea dosing lance is adequately cooled.