The Maintenance Key is found in a toolbox in the underground transport shuttle at the Mars Morimoto Colony along with the Wire Cutters. It is used to open the hatch on the colony's power core in order to deactivate the bomb.
Behind the scenesEdit
As mentioned the key is not found in Pegasus Prime remake. Essentially this item was divided into two items a colony Access Card (used to activate the transport shuttle) and a Power Crowbar used to force the power generator hatch (after using a Nitrogen Canister on it) and a door in the World Science Center.