Mercedes C250- Eco mode not working

it is the battery - the primary one. Please do check in the manual that states only fully charged battery will be able to support ECO function to work. When you press down the brake, the engine will stop and other functions (such as air cond, headlights, etc) will be running on battery and hence your battery needs to be good for the functions. p/s - the battery has to be of same capability/power or more not just any other battery. thanks

I've had this exact issue before on the same car and it turned out to be the battery not holding optimum voltage.

Reading the manual and from personal experience, the following conditions need to be met.

• Battery voltage above 13v
• Engine at operating temperature (85-95c)
• Transmission temperature and pressure (There is a small electric pump which runs during stop start)
• Brake sensor, get someone to check that with the car in drive and the brake peddle pressed until hold appears that the brake lights are lit, it might be brake position or sensor related.
• seatbelt on? the stop/start system will not engage if you're not wearing your seatbelt.
• Indicators on? My c250 wouldn't stop/start when the turn signal was on. I believe this was to allow a rapid get away at junctions.
• Mine would still go into stop/start even with the a/c on if the temperature was close to the target temp set.

The stop/start system is very complex and includes electric pumps and sensors designed to stop the engine in the perfect place to allow a rapid restart. The pumps continue to pump trans oil or maintain system pressure.

If a battery swap and a long drive doesn't resolve the issue, you'll need Merc to plug the car in or you risk replacing good parts or wasting time.

Remember that stop/start

I agree. My 13 c300 4matic was not working for some time. My brake "hold" mode didnt work either. Finally this AM the FB signal on my car told.me battery was low. I just got started on what was a very weak start. After installation of a new Champion AGM battery, both started working almost immediately. Now works all the time I almost forgot this was an option I did.not want dealer amd 500$ later. Done for $210.00 Hope this helps.