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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 24204
Experience:  Over 15 years experience as a Mercedes dealer technician
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Mercedes-Benz C240 my key wont open or lock my doors

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my key won't open or lock my doors
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


I just need a little more info to assist better.

When you press the button to lock or unlock the doors does the little red light blink on the key at all?

If you stand next to the drivers door and point the key at the handle of the door and hit lock or unlock do the doors lock or unlock at all?

Have the windows been tinted with after market tint at all?

Let me know so we can continue,Thanks Pete!
Customer: replied 5 years ago.

Hi Pete,

The doors do unlock and lock if I am right by the driver door. There is a red light that does come on the key when I press to lock or unlock. We have never tinted the windows they are as they came with the car.





It seems like the infra red portion of the key less entry is working but not the radio signal of the key less entry.

This doesn't sound like a key issue since you have this problem with both keys.

What you can try here to re learn the keys is put the key in the ignition and leave it in for about 5 minutes or so and then see if the key less entry operates normally again,sometimes they can lose their programming and can cause this problem.

Let me know if that works or if this helped.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
Customer: replied 5 years ago.
Do I need to turn the ignition on or just put the key in and leave for 5 minutes ? I tried just putting it in for 5 minutes and it seemed to work better for a moment then went back to having to be right in front of the drivers door,
Usually you can just put the key in and leave it,you can try to turn it on and see if it helps or re learns.

If it did work for a bit then quit you may have a fault with the receiving end of the transmitter and may need replaced.

This would have to be done by a dealer as it has to be setup and programmed to operate properly in your vehicle.If the re learn doesn't correct this condition and both keys are acting up this is most likely what is at fault and may need replaced.

You may also want to check all fuses to make sure none are blown,sometimes when a battery is recharged or reconnected/replaced it can cause a voltage spike which can cause a fuse to blow.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
Pete and other Mercedes Specialists are ready to help you
Customer: replied 5 years ago.
which fuse box should I look at? the keys are doing better but not from far away
I would inspect all fuses in all fuse boxes to see if any are blown and replace as needed.

Let me know if you need anything else,Thanks Pete!
Customer: replied 5 years ago.

Ok Thank you Pete. BTW the keys are working better just can't do distance and I still have to point to the driver door. If I left the key in overnight would that make it work ?

No that usually wont make a difference leaving them in overnight.

This may be the receiving end that has a fault.

I would have the codes read out by a dealer using their sds machine and also have them function test the distance of the transmitters.

Thanks Pete!
Customer: replied 5 years ago.
Thanks Pete ! I was hoping to avoid that but I will check the fuse's first
Sounds good.


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