SL/R231: Key NOT recognized
Thread Starter
Newbie
Joined: Aug 2025
Posts: 14
Likes: 4
2017 SL 550
Key NOT recognized
The problem: Key is not recognized by the car, however, the fob locks and unlocks the doors, raises and lowers windows and top.
But I must remove the start button and insert my key fob to start the car.. Sometimes, after starting the car with the key, I can replace the button
and it will start the next few times.
Any ideas on how I can correct this? Is there a secret way you have to hold your mouth while cranking? Maybe close one eye?
Thanks for the help.
Frank
But I must remove the start button and insert my key fob to start the car.. Sometimes, after starting the car with the key, I can replace the button
and it will start the next few times.
Any ideas on how I can correct this? Is there a secret way you have to hold your mouth while cranking? Maybe close one eye?
Thanks for the help.
Frank
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Joined: Nov 2025
Posts: 477
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From: US
Mercedes SL R231
You definitely want a second fob, but be prepared to take a second mortgage or home equity loan.
The dealer can order an "emergency key" (the metal cut key) based on your VIN with proof of ownership. However, the fob part requires programming with the car present. Should you lose your current key, things get more complicated. You will at least need to have your car towed to a Mercedes dealership. Older cars (2014 and earlier) could have new fobs programmed by a licensed locksmith, but not newer ones.
If you are having to insert and turn the key to start the car, then it could be the battery.
The dealer can order an "emergency key" (the metal cut key) based on your VIN with proof of ownership. However, the fob part requires programming with the car present. Should you lose your current key, things get more complicated. You will at least need to have your car towed to a Mercedes dealership. Older cars (2014 and earlier) could have new fobs programmed by a licensed locksmith, but not newer ones.
If you are having to insert and turn the key to start the car, then it could be the battery.
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Joined: Feb 2021
Posts: 1,419
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From: Nor-Cal
2020 GLC300 -2014 Sl550 - 1997 SL600
While this kind of sounds like an EIS issue.
Your car is way too new for this. And R231s don’t appear too susceptible to this issue, It would be out of the norm, not impossible but out of the norm…
What’s your Mileage? Main battery checked or replaced? Ever had your Aux battery replaced/checked. Not just voltage, but either load tested or resistance tested.
Though your car may start, it still may be out of specification.
Can lead to issues you’re experiencing.
I would definitely get another key. You should have two (at least)
Good Luck
Your car is way too new for this. And R231s don’t appear too susceptible to this issue, It would be out of the norm, not impossible but out of the norm…
What’s your Mileage? Main battery checked or replaced? Ever had your Aux battery replaced/checked. Not just voltage, but either load tested or resistance tested.
Though your car may start, it still may be out of specification.
Can lead to issues you’re experiencing.
I would definitely get another key. You should have two (at least)
Good Luck
Last edited by crconsulting; Nov 8, 2025 at 08:10 AM.
Thread Starter
Newbie
Joined: Aug 2025
Posts: 14
Likes: 4
2017 SL 550
Thanks CR,
Surprising event today.... Had the fob in my pocket and I touched the driver's door handle and the locks popped. Put the fob into the key hole and started the car.
Mirrors unfolded and dash lit up. I let the car run for a couple of minutes and shut it off. Inserted the Start/Stop button and pushed it in. Car started right up.
Go Figure.!!!!
I have thought about getting a second key.... but with my " Face Lift" 2017, I can get a new one only through the dealership for $700.00 . I don't understand it,
I am considering getting the entire ignition key set up. I see I can get them on Ebay for what seems a fair price.
What are your thoughts on that.
Frank
Surprising event today.... Had the fob in my pocket and I touched the driver's door handle and the locks popped. Put the fob into the key hole and started the car.
Mirrors unfolded and dash lit up. I let the car run for a couple of minutes and shut it off. Inserted the Start/Stop button and pushed it in. Car started right up.
Go Figure.!!!!
I have thought about getting a second key.... but with my " Face Lift" 2017, I can get a new one only through the dealership for $700.00 . I don't understand it,
I am considering getting the entire ignition key set up. I see I can get them on Ebay for what seems a fair price.
What are your thoughts on that.
Frank
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Posts: 1,419
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From: Nor-Cal
2020 GLC300 -2014 Sl550 - 1997 SL600
Other problem with second hand FOBS is history. Maybe it’s been washed a few times in the laundry.
You’d be surprised how often that happens!Thats also why I suggested having your main battery (and aux battery) checked, via load test or resistance test.
Have they ever been replaced or are they original?
You probably don’t have XENTRY (factory diagnostic software) but it can also be checked in the charge balance section.
Start with the basics first. In any troubleshooting these cars, first thing the WIS (factory repair manual) always starts with is: check condition of batteries.
I would also get a quote from several dealers if you have that option. The price can vary a few hundred dollars
It’s why it’s important to get BOTH keys when you buy these cars second hand.
When you get the new key programmed, they can also code out any old keys that are “floating around” out there.
Good Luck
Last edited by crconsulting; Nov 8, 2025 at 08:28 AM.
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Member
Joined: Aug 2022
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From: Bainsville, Ontario, Canada
SL 550 (2014) Kia Sorento (2016)
If I remember correctly, any car with the fbs4 security system has to have keys from Germany. Fbs3 was on the 231 up to 2013 I believe. With fbs3 you can get a locksmith to duplicate a key.
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From: Nor-Cal
2020 GLC300 -2014 Sl550 - 1997 SL600
EIS on US R231 2013’s is PN a2319055000 which is FBS4.
(Same part all the way up to 2020)
https://www.mbpartscenter.com/oem-pa...IFJlc3VsdHM%3D
That’s the only PN available for our cars. You can see vehicles compatible with that part number in the link above.
Not sure if the early Euro cars are different. (I don’t believe so)
But unfortunately, there’s no reliable source of keys for us in the US other than dealer
Good Luck
Last edited by crconsulting; Nov 9, 2025 at 11:03 AM.
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Posts: 477
Likes: 187
From: US
Mercedes SL R231
If we look at PN’s for our cars,
EIS on US R231 2013’s is PN a2319055000 which is FBS4.
(Same part all the way up to 2020)
https://www.mbpartscenter.com/oem-pa...IFJlc3VsdHM%3D
That’s the only PN available for our cars. You can see vehicles compatible with that part number in the link above.
Not sure if the early Euro cars are different. (I don’t believe so)
But unfortunately, there’s no reliable source of keys for us in the US other than dealer
Good Luck
EIS on US R231 2013’s is PN a2319055000 which is FBS4.
(Same part all the way up to 2020)
https://www.mbpartscenter.com/oem-pa...IFJlc3VsdHM%3D
That’s the only PN available for our cars. You can see vehicles compatible with that part number in the link above.
Not sure if the early Euro cars are different. (I don’t believe so)
But unfortunately, there’s no reliable source of keys for us in the US other than dealer
Good Luck
Thread Starter
Newbie
Joined: Aug 2025
Posts: 14
Likes: 4
2017 SL 550
I will replace the FOB battery even though I replaced 3 or 4 months ago. Sometimes those batteries sit on the
shelves for quite some time.
Last month the " Accessory " battery was replaced. I am planning on checking the "Starter" battery and if it's even close to
being bad, I'll will replace it.
Then I'm going to bite the bullet and make a visit to the dealer and get an additional FOB.
shelves for quite some time.
Last month the " Accessory " battery was replaced. I am planning on checking the "Starter" battery and if it's even close to
being bad, I'll will replace it.
Then I'm going to bite the bullet and make a visit to the dealer and get an additional FOB.
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From: Milton/Westport, MA USA
me: 2015 SL400 & 2015 ML400; wife: 2022 GLC Coupe; daughter: 2017 GLC SUV
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2020 SL / 2026 GLS
Thats also why I suggested having your main battery (and aux battery) checked, via load test or resistance test.
Have they ever been replaced or are they original?
You probably don’t have XENTRY (factory diagnostic software) but it can also be checked in the charge balance section.
Start with the basics first. In any troubleshooting these cars, first thing the WIS (factory repair manual) always starts with is: check condition of batteries.
Have they ever been replaced or are they original?
You probably don’t have XENTRY (factory diagnostic software) but it can also be checked in the charge balance section.
Start with the basics first. In any troubleshooting these cars, first thing the WIS (factory repair manual) always starts with is: check condition of batteries.
MBWorld Fanatic!
Joined: Feb 2021
Posts: 1,419
Likes: 739
From: Nor-Cal
2020 GLC300 -2014 Sl550 - 1997 SL600
Here you go. (May be in a different area depending on which car you’re scanning and which version of XENTRY you’re using.)
https://mbworld.org/forums/sl-class-...ml#post9091277
