The OM651 is a family of inline-four cylinder Diesel automobile engines introduced by Mercedes-Benz in 2008. The chief goal was to create a common engine design that maximized the parts commonality between the engines manufactured by parent company, Daimler.
One requirement of the design was the ability of the engine to be mounted both longitudinally or transversely. Improved fuel efficiency and compliance with Euro 5 emission standards were also design objectives, with Euro 6 standards being achieved by 2010.
Although all engines have the same 2,143 cc swept volume, engines with various power outputs are produced ranging from 120 ps (badged x180) through 170 ps (badged x220) to 204 ps (badged x250). The 170 ps and 204 ps versions employ a twin-turbo charger with a small, high pressure turbo providing quick boost at low RPM and a large, lower pressure turbo providing increased performance at higher RPM. The 100kW lower output version has only a single turbocharger.