A mechanic friend and I replaced the rotors and brake pads for my 2005 C230K. We did not replace the sensor and the Brake Wear indicator is still showing in my dash. Are you supposed to replace the sensor every time you do the brakes? Or is there a way to reset the sensor somehow?

 

You should if the pads wore down enough to have it touch the rotor.
They are only a couple of bucks each, and if you buy premium pads, they usually come with the pads.