I HAVE A MAJOR PROBLEM

The W220 has approximately 174 000 km. Key used to work, and on occassions would suddenly stop. Key does not unlock or lock. Sometimes it starts and sometimes it does not. The key is working, and i have had the vehicle sent to a dealership for a complete diagnostics. the problem was not present. On returning home, the car again refused to start. i then changed the battery in the car, the car started up. after one day the problem came up again. What should i do. Is there a fuse for the steering lock, before i buy a new unit and key

 

I was having a similar problem with my key fob. I put a small piece of electrical tape over the the negative contact so that it held tight against the battery. It seems to have fixed the problem.