Cummins X12 370

Cummins unveiled the X12 in July 2016, with series production starting in 2018. Despite the name, it is not a revision of the ISX12 but a complete clean-sheet design "from the oil pan up": development began in 2013 in cooperation with Chinese partner Beiqi Foton, where the engine is known as the ISG, and the North American version was around 90 percent re-engineered.

The X12 positions itself as a lighter alternative to bigger 15-liter engines, aimed at long-haul and regional fleets that want to save weight without giving up highway capability.

A key element of the weight-saving concept is a single-module aftertreatment unit that combines the diesel particulate filter and SCR catalyst in one shared housing rather than separate units, cutting further weight compared with the ISX12. Injection is handled by a high-pressure common-rail system; the engine meets the North American NOx limits in force since 2010 through the combination of EGR, particulate filter and SCR with AdBlue dosing.

Cummins has already announced it will replace the X12 with the new X10 from 2026, built to meet EPA 2027 standards — meaning used X12s represent the final generation of this line. When buying used, match the model year to the applicable emissions standard, since SCR calibration changed several times over the production run.