This part appears to be known by many names:
Pressure Regulator Valve, Vacuum Modulator Valve, Pressure Transducer or Change-Over Valve Helpful link to diagnostics: http://www.mercedes.gen.in/mercedes-sprinter-turbo-limp-home-los-diagnosis-fault-finding/
Black polymer/plastic, with three vacuum connections and a two pin electrical plug. This is the exact same original OEM part as sold at a Mercedes dealer for less than 1/4 of the retail Dodge price.
Located at the joint between the turbocharger and the exhaust header pipe.
This is the tapered design, which uses a thick sealing ring. (see below)
Compare to your original before ordering, as there are two different types.
This clamp is used on 2004-2006 5 CYL engines, as well as 2014-2016 2.1L 4 CYL engines