3126 is the first electronic engine offered by CAT for the medium duty. The 7.2L engine was introduced in 1997 as CAT’s first electronic engine for medium duty. In addition to an ECM (Engine Control Module), it uses a HEUI (Hydraulically actuated, Electronically controlled, Unit Injector) fuel pump, and has 3-valves per cylinder. It was three variants based on model year: The original 3126 with a 40 pin ECM was offered for 1997, followed by the 3126B with 70 pin ECM for 1998-2003, and lastly, the 3126E with and upgraded HEUI pump for 2003-04.