When a vehicle's ignition key is turned to the "On" position and no sound can be heard from the fuel pump, then the problem is may be a faulty fuel relay. Replacing a fuel relay is easy, but finding the fuel relay may take a little more time, depending on the make and model of the car. The Mercedes C230 fuel relay location is easy to access.
Park the car and press the boot release button.
Open the boot and use a flathead screwdriver to pry the clips holding the boot carpet in place on the driver's-side wall inside the boot.
Remove the fuse box panel cover screws, using a Phillips-head screwdriver, and lift off the cover, which will expose the rear fuse box and fuel relay. The fuel relay is plugged into the fuse box from the outside, on the side, toward the front of the car.
Keep a spare fuel relay in the glove compartment and a small set of screwdrivers. Replacing a fuel relay takes minutes and can be done anywhere. Having one on hand will prevent you from being stranded.
Never use a fuel relay that is not specifically designed for the year C230 being worked on. The wrong relay can cause serious electrical damage.