I own a C200 2019 Mercedes. Due to my work commitment, I have not driven the car for some time. I tried to use the car today, but it does not start. The dashboard shows this message: "Attention Assist, Last Break 00:00 h ago, system suspended, attention level high".
How can I solve this issue? I tried switching off the Attention Assist, but unfortunately, this is impossible with the engine off, and I cannot turn the car on!
Any help is very much appreciated.

 

Attention Assist has nothing to do with your car not starting. Why it's coming up as the default display I don't know, but the Attention Assist regularly gets suspended if it can't determine well enough if you are paying attention. It's irrelevant after just starting the car anyway. It will try to determine your attention level as you drive, but it will never prevent the car from being started. Most likely your battery drained while you were not using the car, so now it doesn't have enough juice to crank the engine. Hook it up to a charger for a bit and see if it starts, or call roadside assistance.

With a 2019, the AGM battery is about done. They last about 4-6 years. I recently had the battery replaced in my 2019 C63 due to its age. The car started to have some electrical gremlins. Either way, if you don't use the car for a while, its best to hook it up to a battery maintainer or at least use the standby mode that turns off the online service etc. to reduce battery drain. These cars maintain a cellular connection while parked, so just like a smartphone, the battery slowly depletes as it uses power to keep the telematics and communication link awake.

 

does not start = ?
Does not turn over and goes click click?
Turns over but never starts and runs?

check main battery voltage as said above