What a nightmare yesterday was. I had both keys on the kitchen counter and both were missing. My daughter used the clothes washer after I ran a load and found my key fob. I went to test the key on the car, at first it wouldn’t work the door locks either way. I got in the car and at first I couldn’t start the car. I had promised to be at my in-laws with the family in Lancaster so I kept trying. It finally started and all was fine. About 15 miles from home I stopped so my daughter could run into a grocery store to pick up some flowers (I dropped her at the door to this store and waited there). My son got out the rear passenger door and that moment the dash said “No key recognized” and the car won’t start. When my daughter came back and opened the door the horn alarm started and all the lights flashed. I had to walk away 30 ft start over.

I’m sorry but I can’t make heads or tails where the key goes to manually start the car. I found the key symbol where the cupholder is but I don’t know how that is supposed to work - isn’t there some spot to insert the metal key?
Somehow the car started but the warning was still on the dash and as I drove back home to get the other key the car loudly beeped constantly all the way.

I replaced the fob battery, the old one was really corroded. The car started and I drove about 2 hrs. The car was parked for 4 hrs and when we had to leave it wouldn’t start. Apparently unknown to me my son removed the battery to see if it could be any water inside the fob. i discovered He installed the battery upside down. The key fob is still not right and even if it starts it’s completely unreliable. To top it off my other key is missing now. To day is devoted to tearing the house apart looking for that missing key.

I must have some bad karma somehow.

Rich

 

Yes, you put the key where the key symbol is and you start the engine that way. It is meant to be used when the key battery is dead, the car pings the chip I guess there is some sort of communication going on with the chip of the key even if there is no battery or battery is dead in the fob.

That said, washing the fob (or moisture getting in basically) may had impaired this function. The metal key is only used for locking the glovebox and open the door from the driver side handle when the fob is out of battery. There is a hole at the bottom of the handle to push the plastic cover off the handle to insert the metal key.

 

Ok, but lets be clear “Key” means the Fob. If the battery is dead or (the obvious- moisture likely bridges the micro electronics of the fob), how can putting the fob into the cup holder do anything? We are talking about just dropping the fob into the cup holder because I can’t imagine holding the fob against the molded-in symbol of the plastic cupholder would do anything.
So despite what I’ve read - there is NO WAY to start this car unless you have a working fob. It might be a good bet this was the first fob battery installed when the car was assembled in July 2017 so it didn’t take much to kill it.

I just have to be better prepared should a key fob fail for other than washing mishaps down the road

 

Vehicle operation is possible when out of battery:
1. Remove keyhole cover on drivers door handle corner, remove key from fob and unlock door. Alarm will sound when door is opened.
2. Hold fob at the key icon in center console, brake and press start. Vehicle will start, alarm will stop.
​​​​The fob needs to be in working condition as it is not magical, wireless power and data will be transmitted between vehicle and key.
Mercedes keys have some water resistance but not really enough for a clothes washer.
​​

 

RTFM. If the fob (or battery) is dead, the fob has an RFID chip in it. Place the fob in the assigned position and the car will recognize that the key is valid and the car will start.

 

That is not true, another forum member mentioned what I was trying to express, the RFID chip.

 

Any RFID requires a battery , RTFM.

 

I am thinking not.

 

It does not in MB's case given the point of the battery being dead in the key you place the key there to start the vehicle, it is a failsafe. Maybe it isn't a RFID chip but it definitely can be started with a keyfob with no battery.

 

It is RFID. My cats have RFID chips as do my credit cards. No battery required.

 

I had a Mercedes service tech at my place tonight. He confirmed what I already knew for the most part. There are many types of RFID chips, most that can be in animals, security passes, boarder passes just have a number that a reader/sensor picks up and the reader can translate just what that number means. The more complicated RFID need a minor power source. I found my second fob and the tech removed the battery to show me my car wont read my fob. Fobs fail to be recognized when a fob battery falls below 1 volt. Mercedes installed upgrades in later production 2017. This upgrade isn’t expensive so when I texted the Carmax general manager earlier about help replacing the key fob, texted in return when I notified him about the upgrade he will have the corporate office reimburse me if I want to take the car to some shop near me.

 

Sorry to hear that mishap . Well, to your relief in my non Mercedes-Benz make the car can't recognize the keyfob when I place it into the door pockets and open the door . It's not related to the battery either . (Don't ask me why I do that lol )
Well, again to the op's relief : Mercedes-Benz keyfobs are solid not fragile .

 

I was so wrapped up in this mess I didn’t think quick or clearly enough. It completely skipped my thoughts to just drop the fob in a cup of isopropyl alcohol to displace any water and blow it clean using compressed air. Another trick - used it the next day was to nuke cup full of rise. Get it fairly hot and push the fob under the rice. That will pull out any water in a few hours.

 

The dealer tech support showed me how to start the car with a dead battery. You hold the fob to the integrated power button and keep holding the button in, it will start. It wont work on the removable power button you can pul out

 

I miss that removable button but non removable ones in present models look nicer