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Key Fob Resync

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Old Apr 8, 2026 | 02:20 PM
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Key Fob Resync
Can anyone advise the step by step process of resyncing a key fob after replacing the battery? As far as I'm aware, it's the correct battery type and also installed correctly however I'm unable to lock/unlock the vehicle.

I have a C300 Sport with stop/start button (so not able to insert key into ignition like most online comments advise).

Thanks in advance!
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Old Apr 8, 2026 | 03:09 PM
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Originally Posted by Zoskie
Can anyone advise the step by step process of resyncing a key fob after replacing the battery? As far as I'm aware, it's the correct battery type and also installed correctly however I'm unable to lock/unlock the vehicle.

I have a C300 Sport with stop/start button (so not able to insert key into ignition like most online comments advise).

Thanks in advance!
Hmmm it should be automatic though.
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Old Apr 8, 2026 | 06:10 PM
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Originally Posted by W205C43PFL
Hmmm it should be automatic though.
that is right. Absolutely No syncing necessary after coin cell renewal - Not upside down, right?

Problem must be elsewhere... like unstable Keyless noGo ?
Beware of battery "drain by parking" when keyless gets sleepless.
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Old Apr 8, 2026 | 07:34 PM
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Originally Posted by CaliBenzDriver
that is right. Absolutely No syncing necessary after coin cell renewal - Not upside down, right?

Problem must be elsewhere... like unstable Keyless noGo ?
Beware of battery "drain by parking" when keyless gets sleepless.
I wonder if it is a bad battery even though OP said it is a new one. Old batteries may get old after all even just stored on the shelf and it might also be defective to begin with.

Last edited by W205C43PFL; Apr 8, 2026 at 07:37 PM.
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Old Apr 8, 2026 | 07:37 PM
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OP, different model but same idea I guess similar keyfob: https://mbworld.org/forums/c-class-w...ml#post8959680
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Old Apr 8, 2026 | 08:12 PM
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Yes it sounds like a battery coating or bad battery. It should not need any relearn off the fob just too replace the battery so at least the problem sounds like a easy fix.
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Old Apr 12, 2026 | 11:04 AM
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OP, link to another forum member post: https://mbworld.org/forums/w212-amg/...ml#post9280325

Try this process and see if anything helps.
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Old Apr 15, 2026 | 03:05 PM
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OP, did you solve the issue?
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