Mechanic Wiki: BYD Seal All Keys Lost Recovery: LAUNCH X431 X-PROG3 Guide

Step-by-step guide for BYD Seal AKL recovery using LAUNCH X431 X-PROG3. Read/write BCM flash, patch dump via server, and program new keys. Includes troubleshooting and expert tips.

Published/Last Updated: May 26, 2026

Quick Answer / Key Takeaway

Losing all keys for a BYD Seal requires specialized equipment because the immobilizer data is encrypted inside the Body Control Module (BCM/VCU). Using a LAUNCH X431 X-PROG3, you can read the MCU flash (typically an S9S12G128), upload the dump to the LAUNCH remote server for patching, write the patched data back, and then learn new keys via the immobilizer menu. Always back up the original binary file before writing — a single misstep can brick the BCM.

Prerequisites: Tools and Knowledge Required

Before attempting All Keys Lost recovery on a BYD Seal, gather everything you need and assess your skill level.

Diagnostic Device: A LAUNCH X431 PAD VII, X431 V+, or any equivalent tablet with Bluetooth/WiFi connectivity. The main unit drives the software and communicates with the X-PROG3.
Programmer Add-on: The X-PROG3 (X431 Programmer) is mandatory. This tool handles low-level reading and writing of the MCU’s flash and EEPROM. You cannot perform AKL on the Seal with a standard OBD key programmer alone.
Connection Cables: You will need the X-PROG3 master cable, a BDM/JTAG adapter (if bench mode becomes necessary), and an OBDII extension cable. Keep spares in your kit in case a cable fails mid-procedure.
Software: Ensure your X431 has the latest BYD software package installed and that the SmartLink/X-PROG3 app is up to date. An outdated app may not recognize the Seal’s BCM.
Blank Keys: Purchase OEM or compatible smart keys. The BYD Seal typically uses a 47-type chip (Kessy/KEFO system). Confirm the chip type before starting — using the wrong key will lock you out.
Internet Connection: You need a stable internet connection to pay credits and upload the dump to LAUNCH’s remote server. A wired Ethernet connection (via a USB adapter on the tablet) is more reliable than WiFi in some workshops.
Technical Skill: This is an intermediate-to-advanced procedure. You must understand BCM location, CAN bus architecture, and basic semiconductor handling. If you are new to MCU programming, practice on a scrap module first.

Step-by-Step All Keys Lost Recovery Process

First Phase: Preparation and Connection

1. Locate the BCM/VCU

The BYD Seal’s Body Control Module sits under the dashboard on the driver’s side, often behind the glovebox or near the steering column. Some model years place it behind a trim panel. Check a repair diagram for your specific year before disassembly.

2. Power Supply

Connect a 24V/10A regulated power supply directly to the vehicle battery. Do not rely on the car’s battery alone — a voltage drop during the write phase can corrupt the flash and brick the module.

3. Connect X431 to Vehicle

Plug the X431 main unit into the OBDII port. Turn the ignition to accessory mode (press the start button once without touching the brake pedal). The tablet should power up and recognize the vehicle.

4. Launch X-PROG3 Software

On the X431 tablet, navigate to Diagnosis > X-PROG3. The app loads the programmer interface. If it prompts you to update firmware, do so now — but only after confirming the battery is stable.

Second Phase: Reading the Immobilizer / BCM Data

1. Select Vehicle and Module

Choose BYD > Seal > BCM (Body Control Module) or VCU (Vehicle Control Unit), depending on your software version. In some versions, the immobilizer data lives under the VCU option.

2. Select Operation

Pick Read Flash / EEPROM. This tells the tool you want to dump the current memory content.

3. Choose Connection Mode

OBD Mode (Recommended): The X-PROG3 communicates over the CAN bus. This mode is faster, but can be unstable on certain Seal variants. Start here because it is simpler.
Bench Mode (Fallback): If OBD mode fails, disconnect the BCM and bring it to your bench. Use the X-PROG3 jumper cable with the correct pinout: VCC, GND, BDM_RESET, BKGD. Set the programmer to 12V (not 5V) for this module.

4. Initiate Reading

Click Start. The tool begins dumping the internal flash. This takes 5–10 minutes. Do not disconnect any cable during this time. A failed read can leave the MCU in an unstable state.

Outcome: A .bin file (for example, BCM_Backup_Seal.bin) saves automatically to the tablet’s internal storage. Rename it immediately with a unique identifier (date, VIN, mileage) to avoid confusion later.

Third Phase: Data Calculation and Key Generation

1. Back Up the File

Transfer the .bin file to a computer or cloud storage. Keep this untouched original backup — it is your only lifeline if the patched file fails.

2. Use SmartLink (Remote Server)

On the X431, open Remote Diagnosis > SmartLink. Select BYD > Seal > AKL (All Keys Lost). Upload the original .bin file. The system charges 1–3 credits (approximately $10–$30 USD depending on your plan). Check your credit balance before starting.

3. Wait for Server Response

The LAUNCH server analyzes the encrypted MCU dump and returns a patched file. This usually takes 1–5 minutes, but can stretch to 10 minutes during high traffic. Keep the tablet connected to the internet and do not close the window.

4. Receive Patched Data

The server sends back a patched BCM file (e.g., Patched_BCM_Seal.bin) along with Key IDs or PIN codes needed for the key learning process. Save the patched file to a different folder than the original to avoid overwriting.

Fourth Phase: Writing the Patched Data Back to BCM

1. Select Write Option

In the X-PROG3 interface, choose Write Flash / EEPROM.

2. Load Patched File

Browse to and select the Patched_BCM_Seal.bin file. Double-check the file name — loading the original backup instead of the patched file will leave the immobilizer locked.

3. Verify Write Mode

If using Bench mode: Power the BCM via X-PROG3. Set the output voltage to 12V. The module should draw a few hundred milliamps when idle.
If using OBD mode: Confirm ignition is ON and battery voltage is stable. A multimeter on the cigarette lighter socket can help monitor voltage.

4. Execute Write

Click Write. The process takes 3–7 minutes. Do not interrupt power or communication. Even a brief disconnect can corrupt the flash.

5. Success Confirmation

The tool displays “Write Successful.” Turn the ignition OFF, wait 10 seconds, then turn it back ON. The instrument cluster should no longer show an immobilizer warning.

Fifth Phase: Key Learning Process

1. Switch to Key Programming Mode

Exit X-PROG3 and go to Diagnosis > BYD > Seal > Immobilizer > Key Learning. The system is now ready to accept new keys.

2. Insert First Key

You will see a prompt: “Insert key into ignition (or press start button with smart key near steering column).” For the BYD Seal, bring the smart key close to the start button area and press the brake pedal. The system detects it.

3. Add Remaining Keys

You can program up to 4–5 keys in one session. Follow the on-screen instructions to add each key. Important: All keys that the customer wants must be present during this session. The module erases any previously stored keys when you enter learn mode.

4. Exit Programming

Turn the ignition OFF, wait 10 seconds, then test each key. Start the engine with every learned key. Verify remote lock/unlock functions. If a key starts the car but does not lock the doors, you may need to perform a remote synchronization (see troubleshooting below).

Troubleshooting Common Failures

X-PROG3 fails to read BCM ("No Identify" error) – Switch to Bench mode. Check pin continuity for VCC, GND, and BKGD. If the signal is unstable, add a 1k ohm resistor between BKGD and VCC. This stabilizes the BDM communication.
Vehicle starts but key does not lock/unlock doors – Perform a remote synchronization: Press the lock button three times rapidly within 10 seconds while standing near the vehicle. This resets the rolling code.
"Immobilizer active" warning after writing – You wrote the original backup, not the patched file. Re-write the patched file using the write procedure described above.
X-PROG3 credit not deducted but file not generated – Check your internet stability. If using SmartLink, try switching to a different server region (China or EU) in the app settings.
BCM seems dead (no communication) after write – Attempt recovery via BDM/JTAG using your original backup. If the module still cannot communicate, the BCM is bricked and will need replacement with dealer-level coding.

Advanced Tips for Technicians

Server Selection – For BYD vehicles, always use the "BYD China" server when uploading the dump. EU or US servers sometimes have longer queues or lack the latest patching algorithms for Chinese-market models.
Data Verification – Before writing, open both the original and patched files in a hex editor. The patched file should show differences only in the immobilizer region. The checksum typically corrects itself automatically, but you can verify with a tool like CRC Calculator.
Key Chip Type – The BYD Seal uses a 47-type smart key compatible with i8M 9000 or HITAG3 systems. Pre-sync the key using a dedicated key programmer (such as Autel IKEY or Xhorse) before attempting the learn procedure. This eliminates potential communication errors.
Multi-Session Risk – Do not attempt AKL on a Seal that has been partially programmed by another tool (e.g., Autel). The crypto algorithm may become corrupted, and the module might refuse to enter programming mode. In such cases, you must desolder the MCU and use a dedicated programmer (XECU, VVDI Prog) to force a full flash erase.

FAQ

Can I perform AKL on a BYD Seal without the X-PROG3?

No. The BCM uses an encrypted S12G128 MCU that requires a higher-level programmer (X-PROG3, CGDI Prog, or similar) for reading and writing. A standard OBD key programmer cannot bypass the encryption.

Do I need an internet connection for the AKL process?

Yes. The X431 sends the BCM dump to LAUNCH’s remote server for calculation and patching. Offline work is not possible. A wired connection provides the most stability.

Can I use a cheap clone of X-PROG3?

Highly not recommended. Clone units often have poor voltage regulation and can easily brick the BCM. Always use an authentic LAUNCH unit to protect your reputation and your customer’s vehicle.

How many keys can I program?

Up to 4–5 keys. The Seal uses a learn-only module, meaning previously lost keys are permanently deleted. You must program all available keys in a single session.

What do I do if the tool says "Security Access Denied"?

This indicates the BCM is locked by a different tool or has corrupted data. You may need to manually remove the MCU (desolder it) and use a dedicated programmer like XECU or VVDI Prog to perform a full recovery. This is an advanced procedure — consider sending the module to a specialist if you are not comfortable desoldering.

Will this procedure affect other modules (e.g., Electric Window, AC)?

No. The AKL process only targets the immobilizer section of the BCM. All other vehicle functions remain intact. After the successful write, test all systems to reassure the customer.

What is the cost per AKL on LAUNCH?

Typically 1–3 credits, which translates to roughly $10–$30 USD depending on your subscription plan. Check your X431 credit balance before starting the procedure to avoid interruptions.

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/