The fuel pump relay is located in the fuse box in the trunk. To access it, turn the trunk key clockwise and lift the trunk lid. The fuse box is located on the left side of the trunk, behind the carpet. Open the fuse box cover and locate relay K4 which is the fuel pump relay.
2008-2014 Mercedes C-Class (W204)
The fuel pump relay is located in the fuse box in the engine compartment. To access it, open the hood and locate the fuse box on the left side of the engine compartment. It is the black box near the firewall, covered by a plastic lid. Remove the lid, then lift the relay marked "fuel pump" which is the fuel pump relay, straight up to remove it.
