With the aid of a 70% grant from the European Union, PKP IC awarded Newag a Zlotys 76.5m ($US 24.8m) contract in 2013 to rebuild the Bo-Bo locomotives in two differing configurations.

Ten of the locomotives will be fitted with two Caterpillar C18 engines and electric train supply equipment for use on passenger services on non-electrified secondary routes, while the remaining 10 units will be hybrid units equipped with a single C18 engine and a bank of batteries and will replace unrebuilt SM42s on shunting duties at major stations. All 20 locomotives will be delivered by 2015.

In 2007 Newag developed a refurbished prototype rebuilt SM42, designated 6DG, with a single Caterpillar C27 diesel engine replacing the original plus new bodywork and cab on the original underframes. Over 100 of these rebuilt locomotives have since been bought by Polish railfreight operator PKP Cargo.

The SM42 is one of the most numerous locomotive types in Poland and 1822 units were built by Fablok at its plant in Chrzanów between 1965 and 1992.