How to Program Mercedes-Benz GL-Class X166 All Keys Lost Using LAUNCH X431

Published / Last Updated: May 28, 2026

Quick Answer: Programming a Mercedes-Benz GL-Class X166 with All Keys Lost Using LAUNCH X431

If you have lost all keys for a Mercedes-Benz GL-Class X166, the LAUNCH X431 diagnostic tool can program new keys without needing a second working key. Connect the X431 to the OBD-II port, select the correct vehicle and immobilizer system, choose the "All Keys Lost" function, follow the on-screen prompts to erase old keys and learn new ones, then verify the new keys start the engine. You will need an active internet connection, an online subscription for security access, and at least one new compatible Mercedes key. The entire process takes about 15–30 minutes.

If you own or work on a Mercedes-Benz GL-Class X166 (2013–2019) and find yourself staring at a pile of empty key rings, don't panic. The "all keys lost" scenario sounds like a nightmare, but with the right diagnostic tool, you can get back on the road without towing your SUV to the dealership. The LAUNCH X431 series—including the V+, PRO, PAD, and HD models—offers a robust key programming solution that handles this exact situation. I have worked with these tools extensively, and the X431's immobilizer functions are reliable when you follow the correct procedure. Let me walk you through everything you need to know.

What You Need Before Starting

Before you dive into programming, gather these essentials. Missing even one can derail the process halfway through.

• LAUNCH X431 diagnostic tool – Any model from the X431 series works, but make sure it has the latest software updates installed. Older firmware may lack support for the X166 immobilizer.
• Mercedes-Benz GL-Class X166 – This covers model years 2013 to 2019, including the GL350, GL400, GL500, GL550, and AMG variants. The procedure is similar across all trim levels.
• New, compatible Mercedes key(s) – You need at least one key, but I recommend programming two in case one fails later. The key must have the correct transponder chip and remote frequency. For North American models, that is typically 433 MHz; European models often use 868 MHz. Buy OEM keys or high-quality aftermarket options like VVDI or Autel that are compatible with the Mercedes DAS system.
• Internet connection – The X431 relies on online coding databases and security access servers. Use a stable Wi-Fi or mobile hotspot. A dropped connection during programming can corrupt the immobilizer data.
• Vehicle battery in good condition – The car's battery must read at least 12.4 volts. Low voltage is the number one cause of programming failures. If your battery is weak, connect a battery maintainer or jump starter before you begin.
• Security PIN or SCN code – Many X166 models require a 4-digit dealer PIN or a 7-digit SCN code to access the immobilizer. You can obtain this through the X431's online security access function (requires a subscription), from a Mercedes dealership with proof of ownership, or via third-party services like KEYDIY or VVDI.

Step-by-Step Programming Procedure

I have programmed keys on dozens of X166 SUVs, and the process is straightforward once you understand the sequence. Follow each step carefully.

1. Prepare the Vehicle and the Tool

Turn the ignition to the ON position. If you have no key at all, some LAUNCH X431 models can power the ignition through the OBD-II port using a special function—check your tool's menu for "Ignition On" under the Mercedes-Benz diagnostic options.

Connect the X431 to the OBD-II port located under the dashboard on the driver's side. Power on the diagnostic tool and wait for it to boot completely. Ensure the X431 has an active internet connection by checking the Wi-Fi or mobile data indicator.

2. Launch the Mercedes-Benz Software

From the X431 home screen, tap Diagnosis. Then navigate to European → Mercedes-Benz → GL-Class → X166. The tool may automatically detect the VIN. If it does not, manually enter the 17-character VIN found on the dashboard or driver's door jamb.

Select the exact model, such as GL350 or GL550. Choosing the wrong model can lead to incompatible software communication.

3. Navigate to Key Programming

After the vehicle system scan finishes, go to the Immobilizer menu. The exact name may vary depending on the X166's configuration:

• ESL / ELV – For models with a traditional ignition key and an Electronic Steering Lock.
• Keyless Go – For models with a push-to-start button and a smart key.

Select Key Programming, then choose All Keys Lost. This function erases all previously stored key data from the vehicle's modules and prepares them to learn new keys.

4. Perform Security Access

The X431 will likely prompt you for a security code (PIN) or SCN code. This is a critical step. If you have the code, enter it now. If you do not, the tool may offer an Online Security Access option. This requires an active subscription on your LAUNCH account. The X431 will connect to the manufacturer's server, send the VIN, and retrieve the PIN—a process that takes about 30 seconds.

Do not attempt to guess the PIN. Entering too many wrong codes can lock the immobilizer for hours or require a dealer-level reset.

5. Enter Programming Mode

Once security access is granted, the X431 will display on-screen instructions. Confirm the number of keys you want to program (the system supports up to 8 keys, but I usually program 2–3). The tool will then tell you to insert the first new key into the ignition (for ESL models) or hold it near the start button or behind the steering wheel (for Keyless Go systems).

Follow the prompts exactly. The X431 communicates with the key and the vehicle's ECU, ESL, and Keyless Go modules. This process takes 30 to 90 seconds per key. Do not touch the key or turn off the ignition during this time.

6. Program Additional Keys

After the first key is learned, the tool will prompt you to insert or present the next key. Remove the first key and insert or place the second one. Do not turn the ignition off unless the tool specifically instructs you to.

Repeat for each additional key. The tool will confirm each key as it is learned.

7. Finalize and Exit

Once all keys are programmed, the X431 will tell you to turn the ignition off and then back on using one of the newly programmed keys. This step finalizes the key-to-vehicle binding.

Now test each key:

• Lock and unlock the doors using the remote buttons.
• Start the engine. The key should crank and run without hesitation.
• For Keyless Go models, verify that the engine starts when you press the button with the key inside the cabin.

If everything works, disconnect the X431 and close the diagnostic session. You are done.

Detailed Troubleshooting Steps

Even with careful preparation, problems can arise. Here is how to handle the most common issues.

Problem: Tool cannot connect to vehicle

• Check that the OBD-II connector is fully seated and none of the pins are bent.
• If VIN auto-detection fails, manually enter the VIN from the vehicle's documentation.
• Update the X431 software to the latest version. Outdated firmware may not recognize the X166's protocols.
• Verify the vehicle battery voltage is above 12.4V. A low battery can cause intermittent communication.

Problem: "Security Access Denied" or PIN request

• You need the correct PIN. Use the X431's online security access if you have a subscription.
• Contact a Mercedes dealership with the VIN and proof of ownership. They may charge a fee but can provide the code.
• Some third-party key programming services offer PIN lookup for a small fee.
• Do not enter wrong codes repeatedly. The immobilizer can lock you out for several hours.

Problem: Key not recognized after programming

• Confirm the new key's transponder is compatible with the X166. Genuine Mercedes keys work best. Aftermarket keys (VVDI, Autel) are often compatible but occasionally cause issues.
• The key blade must be cut correctly for your specific vehicle. If the key does not turn the ignition lock cylinder, get the blade recut by a locksmith.
• For Keyless Go models, the key must be placed exactly where the X431 instructs—typically in the cup holder or a designated sensor area behind the steering wheel. Check the tool's on-screen diagram.

Problem: Programming fails at 50% or times out

• Battery voltage drop during programming is a common culprit. Connect a battery charger or jump starter to maintain voltage.
• Internet connection loss can interrupt the online portion of the process. Use a stable Wi-Fi or mobile hotspot.
• Radio frequency interference from other key fobs, mobile phones, or nearby transmitters can disrupt communication. Move away from potential sources.
• Restart the X431 and the vehicle, then try again with the ignition firmly in the ON position.

Problem: Tool shows "This function is not supported"

• Some older X431 models or outdated software lack full support for the X166's "All Keys Lost" function. Update the diagnostic software or consider upgrading to a newer X431 model like the PAD VII.
• As an alternative, try using the X431's Special Function → Immobilizer → Add Key. However, this usually requires at least one existing programmed key to be present. If you have truly lost all keys, this option will not work.

Pro Tips for Success

These tips come from real-world experience programming hundreds of Mercedes keys. They will save you time and headaches.

• Always program at least two keys. If one key gets lost or damaged, you will still be able to start the vehicle. Programming a single key and losing it puts you right back in the same situation.
• Use genuine Mercedes OEM keys for the highest reliability. Aftermarket keys can work, but they sometimes fail to sync properly, especially on later X166 models with updated encryption.
• If the X166 has a Electronic Steering Lock (ESL), you may need to manually turn the steering wheel slightly to release the lock. The X431 will prompt you. Do not force the wheel—just apply gentle pressure.
• For Keyless Go models, the key's programming location is often near the center console cup holder or behind the steering wheel. The X431 displays an illustration on screen. Follow it precisely.
• Back up your X431 profile and session data before starting. If the tool crashes mid-programming, you can restore the session and continue without starting over.

Frequently Asked Questions

Do I need any special adapter for the LAUNCH X431 to program GL X166 keys?

No. The standard OBD-II cable that comes with your X431 is all you need. The tool communicates directly with the vehicle's CAN bus system through the OBD port.

Can I program a key if I don't have any existing key?

Yes, that is exactly what the "All Keys Lost" function is designed for. It erases all old key data and allows you to start fresh. However, you will need a security PIN, which may be harder to obtain without a working key. The X431's online security access can retrieve it.

How much does it cost to use the LAUNCH X431 for key programming?

The X431 tool itself is a one-time purchase, ranging from about $500 to over $2,000 depending on the model. The online security access and coding functions typically require an active subscription—LAUNCH offers packages like SmartLink or ProDia that cost around $200 to $500 per year, depending on your region.

Why does my X431 ask for a login/password for key programming?

LAUNCH requires an account and often an active subscription to access secure immobilizer functions. Create an account on the LAUNCH Portal and purchase the appropriate package. Without a login, the tool can perform standard diagnostics but not key programming on modern vehicles.

Is it safe to program keys myself? Could I damage the car?

The risk is low if you follow the instructions exactly. The X431 is designed for professional use, but it includes safeguards. However, interrupting the process—removing the tool, turning off the ignition prematurely, or disconnecting the battery—can corrupt the immobilizer data. That would require a dealership visit to repair. Proceed carefully and without rushing.

How do I obtain the security PIN for a Mercedes GL X166?

You have three options:

• Use the X431's online security access function if you have an active subscription.
• Contact a Mercedes dealership with the VIN and proof of ownership. They may charge a fee (typically $50–$100).
• Use third-party services like KEYDIY or VVDI's online PIN calculation. These often require additional hardware, such as a key programmer tool.

My LAUNCH X431 is an older model (X431 V, not V+). Will it still work?

It may work for basic diagnostics, but "All Keys Lost" programming on the X166 often requires the latest software and hardware compatibility. The X431 V+ and newer models support the necessary protocols. I recommend upgrading to at least the X431 V+ for reliable results.

What if the new key remote doesn't work after programming?

The remote locking/unlocking function is managed separately from the immobilizer. After you successfully program the key to start the engine, you may need to synchronize the remote buttons. Use the X431's Key Remote Programming function, usually found under Body or Central Locking. This procedure takes only a minute.

Can I program a key for a GL X166 that has a dead battery?

No. The vehicle needs a healthy battery—at least 12.4 volts—to power the ECU, ESL, Keyless Go module, and the diagnostic tool during programming. Connect a battery charger or boost the battery before attempting.

Do I need to code the key to the vehicle after programming?

If the immobilizer programming succeeds, the key will start the engine immediately. However, additional features like seat memory, mirror position, and radio presets may not sync automatically. You can use the X431's personalization functions later to customize these settings.

Related Topics & Context

Understanding the different immobilizer systems on the X166 helps you navigate the programming process more confidently.

• ESL/ELV vs. Keyless Go: The X166 either has a traditional ignition lock with an Electronic Steering Lock (ESL) or a push-to-start Keyless Go system. The programming procedure differs slightly in terms of where you place the key and which module receives the commands. Always select the correct system in the X431 menu. For ESL models, the key goes into the ignition lock cylinder. For Keyless Go, you hold the key near the start button or a specific sensor area.

• Alternative Tools: While the LAUNCH X431 is an excellent multipurpose tool, other options exist. The Autel MaxiIM IM608 and the Xhorse VVDI Key Tool are dedicated key programmers that also support Mercedes X166 models. The Mercedes dealership uses SDS/Xentry, which requires a subscription and special hardware. The X431 strikes a good balance between affordability and functionality for workshops.

• Key Types and Frequencies: The GL X166 uses either a flip-key or a smart key. Check the FCC ID on your replacement key to ensure compatibility. North American markets typically use 433 MHz; European markets use 868 MHz. Aftermarket keys must be compatible with the Mercedes DAS (Drive Authorization System) encryption.

• Legal and Ethical Considerations: Only program keys for vehicles you own or have explicit permission to work on. Unauthorized key programming may violate local laws and can void vehicle warranties. Always verify ownership before proceeding.

• Future Upgrades: LAUNCH regularly releases software updates to support newer vehicle model years and changes in encryption. Keep your X431 firmware current. An outdated tool may fail on later X166 models or newer Mercedes vehicles.

For more details on using the LAUNCH X431 for other diagnostic and programming tasks, check out our guide on [link to related guide on similar topic]. And if you need a step-by-step on programming key fobs for other Mercedes models, we have a separate article here: [link to related guide on similar topic].

About the Author: Erwin Salarda is an Automotive Service Equipment Technician based in the Philippines, specializing in computerized automotive diagnostic equipment such as OBD scanners and wheel alignment systems. Since 2012, he has been actively providing technical support, equipment installation, troubleshooting, after-sales

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