The urea injection is in place to control the NOx emmissions. Injecting small amounts into the exhaust post turbo allows for the formation of non-volitile compounds. It forms with the nitrogen oxides and makes inert compounds that can go through the other after treatments. They only have a capacity for so much on board and the quantity used depends on the type and style of driver. It will need to be serviced and maintained by the dealer sometime within the first 100K of the life of the car.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.