SL/R129: keyless/fob RF antenna or module?
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Newbie
Joined: May 2026
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1998 SL500
keyless/fob RF antenna or module?
Trying to get a fob to work with the new-to-us SL500, 1998.
We have one switchblade key that came with the car. Using the physical key in the door lock unlocks/locks the car and trunk, and starts the car... no problem there. Transponder seems to work just fine. The fob itself was DOA when we got it, and I suspected it just needed the battery. Replaced that and got the battery-check light to flash on the fob when pressing lock/unlock. That's as far as I got. No amount of trying to sync the fob to the car has been successful. Tried various procedures outlined in forums, as well as the one in the manual. No joy.
Checked the fob on a cheapo key fob analyzer from Amazon, and indeed the key is putting out a 315Mhz RF signal and IR as well.
Is there an RF antenna somewhere for the keyless entry/fob signal that I should check? I was told there may be multiple antennas and if any one of the fails it causes the system to fail? Not sure whether that's right. I know the older cars had the IR system in the rearview mirror, not sure about the later cars. All the fuses seem fine.
We have one switchblade key that came with the car. Using the physical key in the door lock unlocks/locks the car and trunk, and starts the car... no problem there. Transponder seems to work just fine. The fob itself was DOA when we got it, and I suspected it just needed the battery. Replaced that and got the battery-check light to flash on the fob when pressing lock/unlock. That's as far as I got. No amount of trying to sync the fob to the car has been successful. Tried various procedures outlined in forums, as well as the one in the manual. No joy.
Checked the fob on a cheapo key fob analyzer from Amazon, and indeed the key is putting out a 315Mhz RF signal and IR as well.
Is there an RF antenna somewhere for the keyless entry/fob signal that I should check? I was told there may be multiple antennas and if any one of the fails it causes the system to fail? Not sure whether that's right. I know the older cars had the IR system in the rearview mirror, not sure about the later cars. All the fuses seem fine.
Thread Starter
Newbie
Joined: May 2026
Posts: 4
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1998 SL500
I'm trying to resync the one fob I have to the car. It seems like it's not getting the RF signal at all, none of the sync procedures I've tried has been successful. The fob itself is sending an RF and IR signal on lock/unlock button press. I'm asking what to check on the car itself if I assume the fob is working and transmitting.
Key transponder is fine as I can start and lock/unlock the car with the physical blade.
Key transponder is fine as I can start and lock/unlock the car with the physical blade.
Senior Member
Joined: Oct 2017
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SL600
Ah, OK. Maybe you haven't found the right procedure yet, it differs from time to time as you still know. Maybe this could help: https://mb.clifton.io/r129/?ID=2
Thread Starter
Newbie
Joined: May 2026
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1998 SL500
I'm hoping that's it, rather than something in the car. I'm not terribly optimistic since there are only so many ways to mess up the procedure in the manual (two button presses and moving the key to position 2 should do it)
Ah, OK. Maybe you haven't found the right procedure yet, it differs from time to time as you still know. Maybe this could help: https://mb.clifton.io/r129/?ID=2
Thread Starter
Newbie
Joined: May 2026
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1998 SL500
So far I've gotten nowhere.
I'm considering an immobilizer delete entirely, and just relying on physical keys.
If I can't get the fob to work I'm probably going to at least have spare blade/transponder keys made so I'm not locked out. Wondering what options are for aftermarket keyless entry and whether trying to tie that into the car would be a nightmare.
I'm considering an immobilizer delete entirely, and just relying on physical keys.
If I can't get the fob to work I'm probably going to at least have spare blade/transponder keys made so I'm not locked out. Wondering what options are for aftermarket keyless entry and whether trying to tie that into the car would be a nightmare.
