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Old 01-30-2003, 09:04 PM
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W140 Keyless Entry Problems

Unfortunately it has been one thing after another lately with my car...1996 S420.
The latest is the remote keyless entry system quit working. I'm 99% sure that the key is transmitting (and the battery(s) are new), but nobody's home on the receiving end. It won't unlock the doors, no alarm (that I'm aware of), no lights indicating open (green) or locked (red). The alarm does not appear to be arming when I manually lock the car with the key (again, no lights indicating that it is working). However, the doors lock and unlock normally, the trunk works etc when using the key manually.
I understand that there's a relay that may be a problem...has anyone had experience with this type of problem? I know the MB technicians on this site must have seen something like this...
By the way, I checked the fuse and it's O.K.
Thanks in advance for your help.
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Old 01-30-2003, 09:58 PM
Gilly's Avatar
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
First test the remote. Do this by pressing the button and watching the red window on the front of the transmitter. Hold the button for about 5 seconds, and you should see a "flash" inside the window in the key. If you don't get a flash, either the batteries are dead or incorrectly installed, or the key itself is the problem.
If it does flash, try resynchronizing the key. This is normally done by turning the ignition to ON (not start) then remove the key and try locking/unlocking using the remote. If this is unsuccessful, read the owners manual for the synchronizing procedure, I may have it wrong. Usually this procedure is listed in the same section where it tells you how to replace the batteries in the key.

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Old 01-31-2003, 09:22 AM
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Thank you for your post...
I do have a red light that flashes after holding the button for a few seconds. I'll try to resync the key this morning and will post my success or failure.
Thank you for your response.
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Old 01-31-2003, 09:28 AM
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I forgot to add that I do not have the manual...It was lost several years ago. I need to buy a new one.
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Old 01-31-2003, 12:54 PM
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Join Date: Jan 2003
Location: london
Posts: 17
Transmitter (key) operation seems o.k. If the problem is occuring at all receivers, drivers door, pass door and boot then seems the system requires synchronising.
To synchronise system, point transmitter at a receiver and press transmitter button briefly. Within 30 seconds lock and unlock the vehicle with the car key by the door or boot lock.
P.S there are 2-off fuses for the door module located in the boot aux fuse box. Check them both if problem still persists.
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Old 02-02-2003, 03:15 AM
Registered User
Join Date: Oct 2002
Posts: 188
what sunny said is right regarding resync procedures. However depending the year of your car, there are different resync procedures.

My W140 is done at the door just like what Sunny said.

I know the later model is performed inside the car at the ignation. Try a few combination. If all failed, come back and ask again.

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Old 02-02-2003, 06:18 AM
KenP's Avatar
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Join Date: Dec 2002
Location: Southern New Hampshire
Posts: 418
sync at ignition switch

Hi CK,
Syncro instructions are basically correct. On my 1996 W140 S500, syncro is done with the ignition switch method. I think we have identical systems. Don't have the manual in front of me, but believe the process is as follows:
Point the remote at the rear view mirror receiver, push the button twice, and turn the ignition on within 30 seconds.
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Old 02-03-2003, 08:30 AM
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Thanks for your response(s). I've tried to sync the key per the method listed here and I still have nothing. I'm not sure where to go from here...any suggestions? or is this a dealer issue.
Also, I found a manual on e-bay...should be getting it soon.
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