SL/R231: Key Not Detected
Thread Starter
Junior Member
Joined: Dec 2018
Posts: 43
Likes: 8
From: Texas
2015 SL400
Key Not Detected
Yesterday I took my SL to lunch. Everything worked fine on the way but I noticed when I got out that I couldn't get the doors to lock by pressing the "button" on the door handle. So I clicked the lock button on my fob and went in to eat. When I came out, I grabbed the door handle to open it as normal, but instead the alarm went off (horn started sounding). So I used the unlock button on the fob which killed the alarm and allowed me to open the door. I then hit the start button and drove away normally. I had another errand to run and once again, I had to click the fob button to lock the doors. When I came back out I had to use the fob to unlock and this time, when I tried to start the car, I kept getting the "key not detected" (or something similar) message. I pulled the key out of my pocket, hit the lock and unlock buttons a few times and then the car started. So, I figured my fob battery was low. I hit another store and bought a battery and swapped it out. Went to get back in the car and this time I still got the "key not detected" and was unable to start the car until I removed the "start button" and used the key to physically start the car.
I assume the issue is with the sensor that detects the presence of the right key fob. I'm just wondering is there anything I might try before taking it to the Dealer and letting them rape my wallet? Anyone have this happen in the past and found a solution?
I assume the issue is with the sensor that detects the presence of the right key fob. I'm just wondering is there anything I might try before taking it to the Dealer and letting them rape my wallet? Anyone have this happen in the past and found a solution?
MBWorld Fanatic!
Joined: Dec 2010
Posts: 1,447
Likes: 334
From: South Florida
2013 SL550 (Lux Sport), 2006 CL55 AMG (Muscle). S550 (Wife's Sedan)
If your car came with (2) keys, (as it should have), try the 2nd key. If that works fine, then you know the problem has to do with the transmitter of the 1st key rather than with the sensor/signal receiver, a fuse in the car, or something else with the car itself. Occasionally, something just doesn't initialize right when you start the car, but after letting it sit for awhile and then restarting it again, the problem resolves itself. Happens most often with the radio, but it can happen with other electronics in the car as well.
Assume you have already tried re-inserting the batteries and/or another set of new batteries. Also, be sure the +/- polarity is observed when installing new batteries in the MB Smart Key.
Assume you have already tried re-inserting the batteries and/or another set of new batteries. Also, be sure the +/- polarity is observed when installing new batteries in the MB Smart Key.
Last edited by bob55; Feb 28, 2020 at 01:33 PM. Reason: Abb
Thread Starter
Junior Member
Joined: Dec 2018
Posts: 43
Likes: 8
From: Texas
2015 SL400
If your car came with (2) keys, (as it should have), try the 2nd key. If that works fine, then you know the problem has to do with the transmitter of the 1st key rather than with the sensor/signal receiver, a fuse in the car, or something else with the car itself. Occasionally, something just doesn't initialize right when you start the car, but after letting it sit for awhile and then restarting it again, the problem resolves itself. Happens most often with the radio, but it can happen with other electronics in the car as well.
Assume you have already tried re-inserting the batteries and/or another set of new batteries. Also, be sure the +/- polarity is observed when installing new batteries in the MB Smart Key.
Assume you have already tried re-inserting the batteries and/or another set of new batteries. Also, be sure the +/- polarity is observed when installing new batteries in the MB Smart Key.
