Just bought an 01 C240 - Only first thing in the morning (or maybe 1st time starting for the day) the car is unresponsive to the key fob. I can manually unlock the door, however that sets the alarm off. The car is still unresponsive with the key in the ignition, so the alarm continues. It typically takes several minutes, then - everything works great for the rest of the day. ?????

 

It could be the key fob batteries. A good way to check if the fob is sending an infrared signal is to get your phone out and turn on the camera. Then push the lock or unlock button on the key while lookning at the insert end of the key thru your camera view window. You will be able to see the infrared beam if the key is sending a strong signal. If you cannot see anything or what appears to be a weak signal, your batteries need to be replaced. They are CR2025 batteries.

 

Changing the Key fob battery is very easy. DIY !! You will need 2 CR2025 batteries for each key fob.

 

Batteries won't have anything to do with the key not working in the ignition, it will work without the batteries.