How to Program Mercedes GLA X156 Key with LAUNCH X431 | Step-by-Step Guide

Quick Answer: Programming a Mercedes GLA X156 Key with LAUNCH X431

To program a new key for a 2014–2020 Mercedes-Benz GLA-Class X156 using a LAUNCH X431, you need a compatible device with the X431 IMMO (Immobilizer) software activated. The process involves connecting to the OBD-II port, reading the immobilizer status, selecting either “Add Key” or “All Keys Lost,” and following the on-screen pairing steps. A stable 12V battery and internet connection are essential. If you have zero working keys, the procedure requires online authentication with Mercedes servers, making it more involved than a simple add-key operation.

Why Programming Your Mercedes GLA X156 Key Matters

Modern Mercedes vehicles, including the GLA-Class (X156 chassis, produced from 2014 to 2020), use a sophisticated electronic immobilizer system. Each key fob contains a transponder chip that communicates with the Electronic Ignition Switch (EIS) and the Engine Control Unit (ECU). If the key is not “married” to the car, the engine will crank but not start.

Here are the most common scenarios where key programming becomes necessary:

• Lost or damaged keys – The most obvious reason. A replacement key must be synchronized with the vehicle.
• Key fob battery replacement gone wrong – I’ve seen customers accidentally damage the internal board while prying open the fob. The key becomes useless and requires a new one plus programming.
• ECU or EIS replacement – If either module is swapped, the new unit needs to learn all existing keys.
• Used key from a salvage yard – A second-hand key must be erased and reprogrammed to match your VIN. You can’t simply swap keys between vehicles.
• “All Keys Lost” situation – If you have no working keys (for example, after a break-in where the keys were stolen), you’ll need the advanced “All Keys Lost” procedure.

Ignoring the immobilizer can leave you stranded. That’s why having the right diagnostic tool—like the LAUNCH X431—makes all the difference.

What You Need Before You Start

Gathering the right equipment before you begin saves frustration. Here’s your checklist:

A quick note about the key transponder: Mercedes GLA models built between 2014 and 2017 typically use the ID46 chip, while 2018–2020 models often use the ID48 chip. Check your key fob or consult a dealer to confirm. Using the wrong chip means the key won’t communicate with the EIS.

Step-by-Step: How to Program the Key with LAUNCH X431

The exact menu labels vary slightly depending on your X431 software version and region, but the logic remains consistent. I’ll walk you through the standard procedure and the “All Keys Lost” method separately.

Step 1: Prepare the Vehicle and Tool

1. Connect the LAUNCH X431 to the vehicle’s OBD-II port (located under the dashboard, near the steering column).
2. Attach a 12V battery maintainer to the car’s battery. Do not skip this – a voltage drop mid-programming can corrupt modules.
3. Turn the ignition ON (position “2”). If you have no key, use an auxiliary power source or a programming coil.
4. Launch the X431 Immobilizer or Diagnostic software on your device.
5. Select Mercedes-Benz → GLA-Class (X156).
6. Accept any software updates if prompted. A current version is critical for server communication.

Step 2: Enter the Immobilizer Function

1. From the main menu, choose Immobilizer / Key Programming.
2. Select Read Immobilizer Status. This confirms communication with the EIS and shows how many keys are currently learned.
3. You’ll see two main options: Key Learning (for adding a new key when you have at least one working key) or All Keys Lost (for when you have zero functional keys).

Step 3: Authenticate the Operation

• The tool will likely request a Dealer Login. This is an online authentication step.
• The X431 will attempt an automatic Online Login using your internet connection. If it succeeds, you’re good to go.
• If the online login fails (common with older software versions or in regions with limited server access), you may need a 12+12 digit code from a locksmith service or the dealer. Some LAUNCH X431 devices offer a Manual Login option where you enter this code.

Step 4: Program the Keys – Standard Procedure (Add Key)

Use this method if you have at least one working key and want to add an extra one.

1. Insert the first existing key into the ignition and turn it to position “2” (ignition on). The dashboard lights should illuminate.
2. Remove that key and insert the second existing key (if you have one). Again, turn to position “2.”
3. Insert the new key and turn to position “2.”
4. The X431 screen will display “Learning Key Successful.”
5. Remove the new key and test all keys: lock/unlock doors, start the engine. All previously learned keys should still work.

Tip: If you have only one existing key, you can still use this procedure. Just insert the same key in steps 1 and 2, then the new key in step 3. The tool counts inserts, not unique keys.

Step 5: Program the Keys – All Keys Lost

This is the more complex procedure. It requires reading the EIS/ECU data, resetting the learned key list, and writing the new key’s transponder.

1. From the immobilizer menu, select All Keys Lost.
2. The tool will prompt you to place the new key inside a programming coil (often an external antenna that comes with the X431 IMMO kit). If you don’t have one, some X431 models can read the key via the ignition barrel, but the coil method is more reliable.
3. The software reads the EIS and ECU, then erases all stored key IDs.
4. Follow the on-screen instructions to write the VIN to the new key transponder.
5. Once the write is complete, remove the key from the coil and insert it into the ignition. Turn to position “2.”
6. The X431 will confirm that the new key is learned. This key will now be the only key that starts the car. If you need multiple keys, you must add them in subsequent steps using the standard procedure.

Important: The “All Keys Lost” procedure usually requires an active online subscription and server access. If your X431 cannot connect to the Mercedes server, you may need to contact LAUNCH support or a professional locksmith with dealer-level tools.

Common Troubleshooting & How to Fix Them

Even with a quality tool, things can go wrong. Here are the most frequent issues I’ve encountered and how to resolve them.

Problem 1: “Communication Error” with the EIS

• Cause: Low battery voltage is the #1 culprit. The EIS draws a surprising amount of current during programming.
• Fix: Connect a 10-amp battery charger or maintainer. If you’re using a jump starter, ensure it’s rated for continuous current. Restart the X431 and retry.

Problem 2: “Dealer Login Failed”

• Cause: Expired IMMO subscription, incorrect server region, or outdated software.
• Fix: Check your X431 subscription status (you need an active IMMO package). Update the LAUNCH X431 software to the latest version. Try switching the server region (e.g., Europe vs. USA) in the settings menu.

Problem 3: Key Learns but Engine Does Not Start

• Cause: The key transponder is not being read by the EIS. This can happen if the key is a non-genuine aftermarket part or if the transponder chip is damaged.
• Fix: Verify the key’s battery is fresh (most Mercedes fobs use a CR2025 battery). Ensure the key is a genuine Mercedes unit or a high-quality replacement with the correct chip. For a used key, perform an Erase Key procedure first (available in the X431 IMMO menu) before programming.

Problem 4: Tool Freezes During “All Keys Lost”

• Cause: Software bug, interrupted internet connection, or USB cable loose.
• Fix: Close the X431 app completely, restart the tablet, and reconnect to the vehicle. Do not disconnect the OBD cable while the tool is writing data – this can corrupt the EIS. If the problem repeats, contact LAUNCH technical support. In rare cases, you may need to reflash the X431 firmware.

Frequently Asked Questions

Can I program a key for my Mercedes GLA X156 myself with a LAUNCH X431?

Yes, but only if you have the correct X431 device with an active IMMO subscription and a stable internet connection. This is a professional-level tool – not a simple plug-and-play scanner for amateurs. That said, with careful attention to the steps, many DIYers and small shop owners successfully program keys at home.

Does the LAUNCH X431 work for all years of the GLA X156?

It works for models from approximately 2014 to 2020. Later models (2021+) use a different security system with encrypted communication that often requires dealer-level online authorization. For 2021+ vehicles, the LAUNCH X431 may still perform diagnostics, but key programming is more limited.

Do I need the original keys to program a new one?

Not necessarily. The LAUNCH X431 has a dedicated All Keys Lost function. You can program a new key even if you have zero working keys, but the process requires an online server connection and is more involved. For a simple “Add Key” operation, you need at least one working key.

Will programming a key erase my existing keys?

It depends on the procedure you choose. If you use All Keys Lost, the system erases all previous key memories. You must then program all keys you want to use (including the old ones, if you recover them). In the standard Add Key procedure, existing keys remain active – only the new key is added.

Why does my LAUNCH X431 say “No Connection” to the EIS?

First, check that the OBD cable is fully seated. Try a different protocol in the X431 settings (e.g., switch from CAN to ISO). Ensure the vehicle’s ignition is in position “2” (not just accessory). The most common cause, however, is a weak car battery. Connect a charger and try again.

Can I use a used key from another Mercedes?

Yes, but it must be erased first. The LAUNCH X431 can typically read and erase a used key’s data, making it “blank” for your car. This is often a two-step process: first, use the Erase Key or Read Key function to clear the transponder, then proceed with the standard programming steps. Used keys from a different chassis (e.g., C-Class key for a GLA) may not work due to different transponder frequencies.

Final Thoughts

Programming a Mercedes GLA X156 key with a LAUNCH X431 is absolutely doable with the right preparation and patience. I’ve performed this procedure dozens of times, and the most common pitfalls are low battery voltage and an outdated X431 subscription. Invest in a good battery maintainer, keep your tool’s software updated, and always have a spare key blank on hand.

If you run into a roadblock that you can’t solve, consult the official LAUNCH documentation or reach out to their support team. For complex “All Keys Lost” jobs on newer vehicles, don’t hesitate to call a professional locksmith with dealer-level capabilities. The cost of a tow or a damaged EIS far outweighs the price of expert assistance.

For more details on selecting the right LAUNCH X431 model for your needs, check out our guide on [link to LAUNCH X431 buying guide]. And if you’re just getting started with automotive diagnostics, our article on [link to OBD scanner basics] will help you choose the right tool for your workshop.

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 service, and hands-on training for automotive service equipment used by workshops and automotive professionals.

He has received specialized training from international suppliers and manufacturers, including Launch X431 in Shenzhen, China, Lawrence Engineering Company in Guangzhou, China, and 3Excel Wheel Alignment Company in Shenzhen, China. Through these trainings, he developed advanced expertise in automotive diagnostics, calibration, wheel alignment systems, and computerized automotive service technologies.

Erwin Salarda provides professional after-sales support and technical training for automotive diagnostic and wheel alignment equipment, helping clients maximize the performance and proper use of their tools and systems. His experience covers equipment setup, software updates, calibration procedures, troubleshooting, and operational guidance for automotive workshops and service centers.

With more than a decade of experience in the automotive equipment industry, Erwin Salarda continues to support automotive businesses by delivering reliable technical expertise and practical training solutions.

For inquiries and equipment purchases, please visit https://carlifterph.com/

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