remote key won't unlock doors - Mercedes-Benz Forum
 
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#1 (permalink) Old 04-18-2010, 10:32 AM
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remote key won't unlock doors

My 3 button remote will not unlock the doors and trunk on some days. Other days it works fine. Changing the batteries does not make a difference.
At times I have had to use the blade key to get into the car.
No problem using the key to start the car.
My second remote key works fine for all functions.
Is there a way to fix this key or am I looking at getting a new key soon?
Thanks. Paul
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#2 (permalink) Old 04-18-2010, 10:49 AM
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When starting the car

the key gets its power from the inductive process from the cars battery.
Either your key battery is making poor contact or the key is failing.
Check and clean battery contacts in the key.


00-02 drivers side self dimming heated mirror
17mm special spark boot tool
O2 plug and play sensors
16mm spring loaded swivel spark socket
trans dipstick and magnet


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#3 (permalink) Old 04-18-2010, 01:20 PM
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Just replace the batteries in the key.

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#4 (permalink) Old 04-18-2010, 01:30 PM
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Quote:
Originally Posted by daddi View Post
Just replace the batteries in the key.
If the red light on the key fob comes on when you press the lock/unlock button then the battery is fine.

The key has two components to it. A radio frequency component that operates the locking/unlocking of the car and an infrared component that starts the car. It is possible for either component to fail exclusively of the other. The fact that your other key works, suggest that the radio frequency component chip is done for.
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#5 (permalink) Old 04-18-2010, 02:08 PM
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The Ir and

the Rf both open the doors. Thus the Ir receiver in the door handle.
Radio frequency does not need a little red plastic window to transmit its high frequency short distance waves into

If you clean the battery contacts make sure not to touch them or the battery contact points with bare hands.
Also you might try inserting the key in the ignition and let it sit there for a bit to resynchronize the unlock/lock function per factory protocol.


00-02 drivers side self dimming heated mirror
17mm special spark boot tool
O2 plug and play sensors
16mm spring loaded swivel spark socket
trans dipstick and magnet


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Last edited by ohlord; 04-18-2010 at 02:24 PM.
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#6 (permalink) Old 04-18-2010, 07:59 PM
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Thanks for the suggestions.
This is what I have found. The red light flashes strong on the remote that works and very weak on the bad remote. If I switch the battery holder between remotes, then the good remote still works and has a strong red flashing light, regardless of which battery holder is in it. So the problem does not seem to be with the batteries or the battery holder but with the rest of the key.

But after switching the battery holders between the 2 keys a few times, now both remotes work and light up strong. So there may be an intermittent contact issue.

Anyway both keys are working at this time. I hope they stay working.

Paul
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#7 (permalink) Old 04-19-2010, 01:20 AM
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Just for the protocol - I remember that you can start the engine without batteries in the key, because it's powered by the car (induction). So there is a way to open your car even if you don't have batteries - just pull out the mechanical key, open the drivers door with it (the alarm turns on), quickly go into the car and insert the smart key (the alarm goes off). Unfortunately, you can't engage the alarm without batteries.
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#8 (permalink) Old 05-18-2014, 08:49 PM
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i have a 2003 mercedes S500, today i tried unlocking my door with my key fob, but never worked. i used the metalic key to open door, when i put the fob key into ignition , it didn't work . the fob light never lit up, when pressing on its buttons . the front console system was working. even though the batteries where fairly new, i changed them to brand new batteries , and again fob key didn't work and red light never turned on. also, last time i used key fob was 2 days ego , and there was a huge rain storm here in new york , maybe it got wet, there is a small hole in the fob key casing, but its been there for a long time, with no issues . what can i do ???
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