The Caterpillar 3126 is a turbocharged 7.2L inline 6-cylinder diesel engine manufactured by Caterpillar and first introduced in 1997; it was the first electronic mid-range diesel engine that Caterpillar produced. It is the successor to the Caterpillar 3116 engine and was replaced by the Caterpillar C7 engine in 2003. It is a medium-duty engine and has been used in dump trucks, long haul trucks, ambulances, buses, RVs, boats, cranes, fire trucks, and more. In 1998, Caterpillar released an improved version, the 3128B; in 2002, the 3126E was released; though these improved versions only affected engine electronics, not the actual engine design. Caterpillar launched a three-tier system of overhaul kits for the 3126 and its C7 successor in 2011.
It was rated for multiple power applications from 170HP to 330HP.