My key fob does not lock or unlock the car any longer.

Problem started two months ago, and I found that the batteries were too weak. Replace both of them and the fob would not flash the IR light. I used my cell phone camera to check for output of the IR LED - found the LED was bright constantly.

So, I removed the new batteries and after ten minutes, reinstalled them and then drove the care for a few minutes. Found the fob was now working again, and would lock and unlock the car normally.

A couple weeks later - the key fob came apart when my wife was trying to start the car, so I reassembled everything, but the IR LED would not turn off again. Tried removing the batteries and letting it sit again, but this did not solve the problem. Now, the IR LED stays lit and drains the batteries after several days.

I tested the single push-button switch in the fob and it appears to be working properly (not shorted) as I hear it click when depressing it - while the fob is disassembled.

Have spoken to Mercedes numerous time and they are giving me the run around; NO vendor to repair, or replace the fob. I got a call from them yesterday saying that a press release will be released in Sept about what they are doing to solve the problem.

So, does anyone have any suggestions about repairing the key fob?

Thanks for any replys.

Near as I can tell, no car manufacturer repairs remote fobs beyond changing a battery.

E bay vendors are selling single button remote housings ( no internals ) . There are two versions, narrow and wide key but you should be able to reuse your key bit.

When turning the key, hold it close to the ignition lock, this reduces pressure on the housing and keeps it from coming apart. If the key is difficult to turn, the lock will need attention as once it binds up and won't turn, it is a real mess to cut apart.

Have you removed the circuit board from the housing, installed a battery and checked for output? Perhaps the housing is holding the switch on.

If the remote has gotten wet, ( even in a pocket on a sweaty day ) minerals / salts can build up on the circuit board causing all sorts of unintended operation.

These remotes have a battery check function that flashes red visible light after the button has been held for 5 or so seconds. Do you have visible light when the IR LED is in operation?

Near as I can tell, the older remotes like yours are not locked to the car so getting a used one is possible. ( 97 + has a RFID chip that locked to the anti theft box and ECM, if the chip is transferred a 97 can accept a used remote. ) The sync procedure is 2 clicks of the remote, insert key into ignition then turn the run position.

97 SL320 - thank you for the reply. I will double check for "bridging" on the key fob circuit board. I did not yet try to activate the fob outside of the housing - but will try this too.

As for the security - all S Class fobs have the encription built into the IR pulses and they ONLY work with the car which they were originally programmed for - according to Mercedes.

Also, I have not tested the battery check function, but suspect it will not operate until the IR LED will turn off. But I will try this too.

Thanks again for your input.

Good news! I cleaned the circuit board and now the fob is working! Thank you very much 97SL320!!

Just a followup - my wife dropped the fob ad it quit again! Can not get it working again.

Talked to MB again, still no word about a source for a new fob!

Any thoughts from anyone?

Thanks in advance.