W211 key fob problem

dursleyman

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One of our key fobs has just refused to unlock the car. There were no prior symptoms, the other one still works fine and both are regularly in use. I have replaced the batteries and it will now unlock and lock the car OK but the car does not seem to recognise the key in the ignition. You do not get that click/buzz sound when you put the key in.

I discovered that the car does recognise the key if I press the unlock button with it in the ignition and the car will then start OK, but I have to repeat this every time.

Ideas please.
 

Craiglxviii

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Call RMK in Birmingham- replacementmercedeskeys. What they don't know ain't worth knowing.
 

LostKiwi

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Does the key rattle if you shake it? If so the RF coil in the base of the key has become detached (typically key dropped).
 
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dursleyman

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Does the key rattle if you shake it? If so the RF coil in the base of the key has become detached (typically key dropped).

No nothing like that. No other clues at all. I have tried the IR check using a cellphone camera and that does appear to be working. Its just that the car does not seem to know when its in the ignition until I press the unlock button with it in.
Got an hours run with the car tomorrow so I will set off using the problem key and see if a miracle happens on the way. The "good" key will be along just in case.
 

LostKiwi

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The key has two methods of communication with the car - IR and RF (radio).
By default it will use radio when the key is inserted into the lock. The car transmits a signal which is received by the coil in the bottom of the key and the key responds (again using the coil). When you push the button you operate the IR and RF but if the RF isn't working IR will unlock the car (you can test this by covering the end of the key and trying to unlock it or face away from the car and try). If it fails to unlock the RF is definitely not working.
When you put the key in the lock the RF operates automatically but if it fails then pushing the button will operate the IR and the lock will function.
 
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dursleyman

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Update on the key mystery. I have tested the RF by locking/unlocking with the key covered up and in my pocket so that seems to confirm it is working for that function anyway. The IR does show by using the cellphone camera test so that seems OK.
The car still does not respond when I put the key in the ignition, but pressing either of the lock or unlock buttons with it inserted and its good to go. I have done about 50 miles in the car today by using this method but the problem is still there.

Is there some other way I can prove what is going on or do I invest in a new key. Bit reluctant to spend the £250 or so unless it will definitley fix the problem.
 

LostKiwi

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My bet is still the coil in the base of the key. RMK as Craig suggested are the people to talk to.
 
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dursleyman

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My bet is still the coil in the base of the key. RMK as Craig suggested are the people to talk to.


I have messaged them with the problem and I will report back how it goes.
 
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dursleyman

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Spoke to MRK and posted the key to them on Monday. It came back today fixed - actually I think its a new one - but it works and that's all we ask.
Total £90 plus P&P and vat so really good service I think.
 
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