I cannot find C240 on your list of models so I have chosen a C230 from that list. It is a 1998 model. One of my 2 keys does not get used very often and for the last 12 months or so the red light on that key was flashing but the key has only worked after twisting it a number of times in the ignition for it to activate. Sometimes the car could be locked and unlocked. Thinking it probably was the batteries, I replaced them with 2 new CR2025. The red light flashes when any of the 3 buttons are pressed but it will not activate the ignition at all or open or close the doors.