My key FOB On my 2012 E550 is not working and I only have one. When I push a button on it a little red light by the panic button flashed. Any ideas?

 

Could you please be more explicit on what is NOT working? The keyfob provides lots of functionality
1 - Can it open the doors when clicking?
2 - For KeylessGo, can you open the door by only pulling the handle w/o clicking in the keyfob?
3 - For KeylessGo, can you start the engine by just pushing "Push-Start" on the console?
4 - If you insert the key in the ignition, is it recognized?
5- Can you turn the key on the ignition?
6 - Does it crank, if (5) passes?

 

Thanks for the reply. I have Keyless Go. I have some power when I get in the car, but the key fob will not activate anything. The key in the ignition will not work either. If the car battery is dead, should I still be able to lock and unlock the doors?

​​​​​​​I was messing with the car this morning and accidently left the headlights on for 6 hours. When I came out the car would not start. IOs it possible the battery is dead to the point the FOB will not activate anything?

 

indeed, if the car battery is dead, the vehicle locks will not work. use the mechanical key to open the drivers door, open the hood, and put a decent quality charger on the battery overnight. Do NOT jumpstart and expect the car to recharge the battery, unless you plan on a new battery sooner rather than later, the alternator will dump the fastest charge it can on the battery, and that will further stress it. running a lead acid battery down to flat once probably kills half its working life. I use a NOCO Genius 10 for charging batts, Ctek are also excellent. Those old Schlumberger or Diehard charger things with the analog meters are NOT very good.

 

+1 on not jumping when the battery is flat. I would be more concerned with damaging the voltage regulator ( overheating ) than the nearly death battery which likely due for replacement.
also, never have these keys in the ignition if jumping the vehicle.

Once your battery status is back up, let us know if the key is still an issue.

Nearly everything must always be at the proper levels: oil, coolant, brake fluid, batteries and gas.

Low batteries breed Gremlins into these cars, running on low fuel frequently overheats the fuel pump.

 

So here is the resolution. Prior to all this happening I needed to access the sidelight. In order to do so, I turned the wheel all the way to the right to pull the fender liner back. Apparently the steering wheel locked and would not start the car. Violently pulling the steering back toward center while turning the key solved the problem. Go figure.

 

Careful. Not all W212 use the "mechanical steering lock", so my steering wheel is always free.

Now, that could be a symptom of your steering lock motor starting to quit on you. If it does quit, you will be in pain to remove the lock module. Here is the $12 motor that can make spend $1K plus if failed when installed
Time to monitor it. As I said earlier, careful with voltage swings in these cars.

 

I assumed W212s have a warning for headlamps in case if forgotten . Speaking of steering wheel lock my steering wheel is free too but I don't like to play with those for any car I have driven when the car is stationary

 

With my 2015 SL, I have left my headlights turned on (not Auto) and unintentionally ignored the warning, and they do turn off after a few minutes. This is different from the lights off delay at night. There is both a chime and a visual warning on the dash. However, not so lucky with my 2004 SL500.

I'm guess that "feature" is year and maybe model dependent.

 

on our late W212, we just leave the headlights on Auto all the time. they go out a few seconds after you shut off the ignition, then the DRLs and tail lights dim out a half minute after you lock the car.

 

I believe there are settings you can play with as well for the length of time the lights stay on after locking and which ones stay on and what not. I personally never messed with it and leave it in auto except when passing security checkpoints and have to switch to just parking lights.