2020 Mercedes-Benz SL Key Replacement

2020 SL key specs

The R231 kept a folding hardtop but moved to an aluminum body, and its key system spans Mercedes' switch from FBS3 to FBS4. Many cars have Keyless-Go, with a start button in the dash ignition slot that pulls out so the fob can go in directly. SL550, SL400, SL63 AMG and SL65 AMG versions follow the same layout. The fob carries an emergency key, and because early and late fobs look so similar, the VIN, not the key's appearance, tells us which system the car uses.

What's specific to the 2020 SL

2020 was the final model year of the SL R231, before the R232 arrived for 2022. Late-run cars occasionally pick up running changes, so we check the VIN instead of assuming a 2020 Mercedes-Benz SL matches a 2013. A 2020 Mercedes-Benz SL is about 6 years old now. Original fob batteries are near the end of their life at this age, so weak range or a "key not detected" message is often a battery before it is a failed fob. Cars this age are often on their second owner, which is when a single remaining key and a request for a spare tend to show up.

Smart-key cars like the 2020 SL can be targeted with relay attacks that extend the fob's signal from inside your home, so keep fobs away from exterior walls or in a signal-blocking pouch, and have any missing fob erased from the car.

Key options for the 2020 Mercedes-Benz SL

• Remote head key. A remote-head key puts two separate systems in one piece: a cut blade with a transponder chip that the immobilizer reads, and a small circuit board with buttons that signals the body control module to work the door locks. On a 2020 Mercedes-Benz SL with this style of key, each side is programmed separately. That explains some confusing failures. If the remote stops working but the car still starts, the problem is usually the battery or the remote board. If the buttons work but the engine won't run, look at the chip side. Knowing which half failed tells us whether you need a repair, a reprogram or a whole new key.
• Smart proximity key (push-to-start). A smart or proximity key lets a 2020 Mercedes-Benz SL open when you touch the door handle and start with a push of a button while the fob stays in your pocket or bag. Antennas in the doors and cabin send out a low-frequency wake-up signal; the fob answers on a higher radio frequency with an encrypted reply, and the car only allows a start once it confirms the fob is inside. When the fob battery is weak, that conversation fails, which is why most designs include a backup: hold the fob against the start button or set it in a designated pocket. The owner's manual shows where, and it's worth checking before you need it.

How the Mercedes-Benz immobilizer works on the SL

• There was no 2021 model-year SL in the US; the R232 replaced this car for 2022.
• FBS4 keys are built for one VIN, so a used SL fob cannot be recoded to your car.
• A dealer can block a lost key from starting the car.

Programming a 2020 SL key

Early R231s on FBS3 can usually take a spare made by reading the ignition switch and calculating the key password from a working fob, and all-keys-lost may be possible with the switch on the bench. Once the car is on FBS4, keys come only from Mercedes-Benz, built for the VIN and ordered through a dealer, and we don't originate them. A VIN check tells us which applies before we quote, and we can handle lockouts and emergency keys either way.

How we make a Mercedes key depends on that era. FBS3 cars don't learn keys through a simple OBD-II menu. We read the electronic ignition switch, through the diagnostic port when the car allows it or with the switch removed and on the bench, use data from a working key to calculate the key password, and write a new key into one of the switch's free positions. Once written, a Mercedes key is tied to that car, so a used key from another vehicle generally can't be reused. FBS4 keys, found on most models from about 2015 on, are built by Mercedes-Benz for a single VIN and ordered through a dealer, and we don't make them. Keys for the oldest pre-FBS3 cars usually come the same way. Whatever the year, we check your ID and registration, confirm the system by VIN, and tell you before starting which parts of the job are ours.

FBS3 cars can usually get spare keys from us; FBS4 cars need a dealer-ordered key, which we confirm by VIN.

Lost every key to your SL?

1. Gather your documents and the VIN. Call with the year, make, model and VIN if you can read it through the windshield, plus where the car is parked. Those details let us confirm whether your Mercedes-Benz SL can be done on-site and bring the right key, so the first trip is the only trip.
2. Get into the vehicle without damage. Entry comes before key-making because we need access to the ignition, the OBD-II port and sometimes the documents in the glove box. We take care with weather stripping, door frames and paint, and we confirm the dash VIN matches your registration before going any further.
3. Originate a new key from the car. Originating a key means building it without a sample. The door lock usually reveals most of the cuts; any it doesn't are worked out by test-cutting and trying the ignition or a second lock. The finished blade should feel like a factory key, not a forced fit.
4. Program the key to the immobilizer. All-keys-lost programming often takes longer than adding a key, because the car has no trusted key to authorize the change. We follow the procedure your Mercedes-Benz SL requires, then confirm the engine starts and keeps running and the remote or keyless functions respond.
5. Erase missing keys and add a spare. A lost key's metal blade can still open your doors even after its chip is erased. If the keys disappeared along with something showing where you live or park, consider rekeying the car's door lock cylinders too. We'll also recommend leaving with two working keys, not one.

Why a spare key pays for itself

• When you sell or trade in the vehicle, buyers and dealers expect two keys. A missing key can come up during an appraisal or a private-sale negotiation, so having both on hand keeps the conversation about the car, not about what it will cost the next owner to replace one.
• Electronics fail without warning. A fob dropped on concrete, run through the washing machine or soaked at the pool can quit for good. With a second programmed key, that's an annoyance you fix on your own schedule, not a stranded car that needs attention today.
• A spare stored safely at home rescues you from a locked car with the fob sitting on the seat, a key dropped somewhere along a hiking trail, or a fob that stops responding on a busy morning. Keep it indoors, never in a magnetic box under the bumper.

Dealer or mobile locksmith?

The biggest difference between a dealership and a mobile locksmith is where the work happens. A dealer programs keys in its service bay, so if every key is lost, the car usually has to be towed there, and you work around the service department's schedule and the time it takes to order a key by VIN. Julian's Locksmith brings the cutting machine, key blanks and programming equipment to the car, whether it sits in your driveway, a workplace lot or a parking structure. For a 2020 Mercedes-Benz SL we can program on-site, that means no tow and no shuttle rides back and forth. The trade-off is real, though: on vehicles where only the dealer can program keys, a tow or appointment may still be necessary, and we'll say so before you spend anything on our visit.

SL key battery

Most fobs for a 2020 Mercedes-Benz SL open along a small slot in the seam; a coin or a plastic pry tool works better than a screwdriver, which chews up the housing. If the fob hides a mechanical blade, slide it out first, since the case often opens from that gap. Note which side of the old cell faces up, swap in a fresh replacement, and press the halves together until they click all the way around. Handle the new battery by its edges, because skin oil on the faces can hurt contact. In most cases the fob keeps its programming through a battery change, so test lock, unlock and start, and you're done.

How the job works

1. Identify the exact key your SL uses. We ask a few quick questions on the phone: the year, whether the car starts with a turn key or a button, how many keys you have left, and whether the remote still works the doors. Then we check the VIN against our programming references so the van arrives with the correct blank or fob, not a close guess.
2. Verify ownership before any work. Before cutting or programming, we compare your government photo ID with the vehicle registration or title and check that the VIN on the paperwork matches the VIN on the dash. If the registration is locked inside, we open the car first, confirm the documents, and only then make the key.
3. Get the key code or decode the lock. If you still have a working key, we can read its cuts directly and check them against the factory depths for the Mercedes-Benz keyway. A worn key gets corrected back to spec during this step, so the new key turns crisply instead of reproducing years of wear in a fresh piece of metal.
4. Cut the blade on-site. Our van carries a code-cutting machine that handles both traditional edge-cut blades and the laser-cut, side-milled profiles common on newer keys. The blade is cut to the code, then test-fitted in a door lock and the ignition or emergency keyhole to confirm smooth operation before any programming begins.
5. Program the chip, remote or smart key. Programming tells the car's computers that the new key belongs to the vehicle. Transponder chips are added to the immobilizer, remote buttons to the body control module, and proximity fobs to the keyless system. If a step requires dealer-only access on your SL, you'll have heard that before we arrived, not halfway through the job.
6. Test everything and clear out old keys. The last step is a short walkthrough. We show you how many keys the car now recognizes, point out the dead-fob start method for your vehicle, and hand you an itemized receipt. If a spare makes sense, it's simplest to add it during this same visit while the equipment is already connected.

What affects the price of an SL key

• The type of key. The biggest factor is technology. A plain mechanical key is a cutting job only. A transponder key adds a chip and programming. Remote-head and flip keys add a circuit board, and a proximity fob for a push-button Mercedes-Benz SL is the most involved of all, both in the part itself and in the programming.
• Programming complexity and security access. Two cars with similar-looking keys can program very differently. Newer platforms often guard key programming behind encrypted access or paid credentials, while older systems allow straightforward OBD-II pairing. We check the exact procedure for your VIN before quoting, so the number reflects the real work involved.
• Blade style and cutting. The blade still matters on keyless cars, because the emergency insert has to fit the door lock. Cutting by code is standard for us. Decoding a door lock when no key or code exists adds time, and so does progressing any cuts the door lock doesn't show.
• Travel, timing and extra repairs. Sometimes a key problem is really a lock problem: an ignition that won't turn even with the right key, or a door cylinder that has been jammed for years. Fixing those is separate work. We point them out, explain the options, and quote the whole job up front so the bill holds no surprises.

Call (951) 903-3193 with your VIN and the keys you still have, and we'll quote the job before any work starts.

Tips from a mobile locksmith

• Never hide a spare key or fob on the outside of the car. Magnetic boxes in wheel wells and under bumpers are the first places a thief checks, and with a proximity fob, a hidden key can let anyone open the doors and drive away. Keep the spare at home or with someone you trust.
• When a key's head cracks or its blade bends, replace it before it fails. A transponder chip can slip out of a split head, and a bent blade can break off inside the ignition or door lock, turning a simple key replacement into an extraction and repair job. Small symptoms are the inexpensive time to act.
• Be careful with discount fobs from online marketplaces. A listing may match your remote's shape while using a different frequency, chip or FCC ID, and many used smart keys are locked to their original vehicle. If you already bought one, send us the listing or a photo before the visit so nobody pays for a programming attempt that can't work.
• If your vehicle has a proximity key, think about where it sleeps at night. A fob hanging by the front door can sit within range of relay equipment used to open and start cars from outside. A drawer deeper inside the house, a signal-blocking pouch, or the fob's own sleep mode reduces that risk considerably.
• Learn your car's dead-fob start method now, in the driveway, rather than in a dark parking lot later. Depending on the make, you hold the fob against the start button or place it in a marked pocket in the console. Also find the hidden keyhole on the driver's door handle and practice using the emergency blade.

Proof of ownership

Before we cut or program a key for any vehicle, we verify that you have the right to it. Please have two things ready: the current registration or the title, and a government-issued photo ID with a matching name. We also check that the VIN on those documents matches the VIN plate on the dashboard. If the registration is locked inside the car, that's fine; we open the vehicle first, check the paperwork in the glove box, and only then make the key. If something doesn't line up, we stop and sort it out before any key is made.

Need a 2020 Mercedes-Benz SL key?

Locked out, keyless, or just tired of a fob that only works half the time? Julian's Locksmith can help with your SL in Southern California. Have your registration and photo ID ready, call (951) 903-3193, and we'll give you an honest answer about what we can do on-site and what it will cost before we head your way.