Key Fob Not Working? Try This!

[Slartibartfast]

Just fixed my non working key fob using information found here:

Mercedes Key Fob Not Working?

Thought it may be useful for anyone with a key fob problem

 

[Diesel Benz]

Fixed your S350 key even if the car does not have any AAM module?

 

[Slartibartfast]

Fixed your S350 key even if the car does not have any AAM module?

I got home today and clicked the "lock" on the key but nothing happened. Unlock and Boot release also not working. I changed the battery (new Duracel 2025) and tried again but not working. I then followed the instructions (from the above link):

1. Put the key in the ignition.
2. Quickly remove it within 10 seconds and hold down the Lock button.
3. While holding the Lock button, press Unlock five times.
4. Release these buttons and press the Trunk button once. This should synchronize your remote. You will be able to tell if it worked by pressing the Lock and Unlock buttons to see if they work.

The key fob now works perfectly.

 

[Diesel Benz]

Sorry but to me this guide is similar to having the key and shaking it while walking around the car twice clockwise and then once counter-clockwise and then pressing the key buttons a few times until they work. The MB key has not needed any sync with the car since the old "IR keys".

Never know if there is a sw bug that gets overcome by a funny procedure like the W211 rear SAM SW got confused at times and only recovered from a power reset (or reset with star).

Show me a workshop instructions document explaining what this sync does and I might change my pessimistic view.

 

[Slartibartfast]

Sorry but to me this guide is similar to having the key and shaking it while walking around the car twice clockwise and then once counter-clockwise and then pressing the key buttons a few times until they work. The MB key has not needed any sync with the car since the old "IR keys".

Never know if there is a sw bug that gets overcome by a funny procedure like the W211 rear SAM SW got confused at times and only recovered from a power reset (or reset with star).

Show me a workshop instructions document explaining what this sync does and I might change my pessimistic view.

Maybe it was just coincidence that it worked for me? I don't have any knowledge in this area and I appreciate your input. Not sure how I can remove the above link and "instructions" now as the "edit" button is not available. Thanks again

 

[Diesel Benz]

Don't think there is any need to remove the link. On the contrary, better to have it for others to read. More comments from other forum members welcome.

 

[Slartibartfast]

Don't think there is any need to remove the link. On the contrary, better to have it for others to read. More comments from other forum members welcome.

Cheers, just don't want to be giving out bad info

 

[mioba]

Could be the key just lost its sync. Merc are rather sensitive with this info as keys are normally
only available from Germany after providing DNA samples

 

[Diesel Benz]

Could be the key just lost its sync. Merc are rather sensitive with this info as keys are normally
only available from Germany after providing DNA samples

Are you referring to the rolling code sync? Mercedes is not really sensitive on keys related info except that they do not share customers details that customers can do nothing with. Pairing keys is basically permanent and these days even workshops do not get virgin parts to be paired with any car. As such no sync with the car is needed.

The remote locking is using a rolling code though. One cannot "copy" one command via radio and reuse it later, the rolling code prevents this. I've never faced lost sync with this rolling code and there is not much talk about it on the forums. I guess if the key fob is used too many times away from the car, the accepted rolling code window at the car may not match with the code the key is sending. In this kind of a scenario the rolling code window could be synced as described above. EIS anyway is using a two way challenge/response approach that never loses sync. Once an authorised key is detected by EIS, it would be safe to resync the rolling code window. A bit of cryptic sequence of buttons pressed is needed to avoid unintentional pairing with a foreign key that just happens to be used near by.

More comments welcome, there must be many experts on the forum that are familiar with the topic!