XTOOL M821 Adapter for Mercedes-BENZ All Keys lost Programming
The XTOOL M821 Mercedes-BENZ All Keys Lost Communication Adapter is designed to streamline and optimize all-key-lost programming across multiple Mercedes-BENZ modules. With the M821 Adapter, you can reduce calculation time by up to 65% or eliminate the need to repeatedly plug and unplug a key emulator hundreds of times.
Important Notices
- Requires use with XTOOL KC501, PAD3, or PAD3 SE.
- Ensure your Mercedes-Benz key programming software is updated to the latest version (27.10).
- Mercedes-Benz all-key-lost programming must be performed online. Maintain a stable network connection throughout the process.

XTOOL M821 Adapter Features
- OBD-16 Port: Connects to the J1Z02_BENZ communication cable or links directly to EIS/EZS modules via DuPont cables.
Caution: Do not connect directly to the vehicle’s OBD port. - Status Light: Indicates power status. Red light on = power is active.
- Comm Light: Shows communication status. Blue light on = adapter is communicating with the tablet.
- DB15 Port: Connects to the main cable of XTOOL tablets.
Note: Disconnect the OBD2-16 connector from the main cable before connecting to the M821 Adapter.
XTOOL M821 Adapter Connection Method
- Connect KC501 to the device via USB.
- Attach the Mercedes-Benz IR emulator to the KC501.
- Disconnect the OBD2 connector from the main cable, then connect the device (or VCI box) to the M821 Adapter using the main cable.
- Connect the 12V power supply to the main cable.
- Link the EIS/EZS module to the M821 Adapter using the J1K02_BENZ cable. Refer to your device for specific connection details.
Note: Consult the diagrams on your device when connecting the M821 Adapter and EIS/EZS module via the J1K02_BENZ cable.
Note: The Mercedes-Benz IR emulator must remain inserted into the module slot during operation.
Note: For devices equipped with a VCI box, connect the M821 Adapter to the VCI box using the main cable, and keep the VCI box paired with the device via Bluetooth. Refer to your device for detailed instructions.

Supported EIS Modules
- W164 (OLD)
- W166
- W204
- W212 (NEW)
- W164 (NEW)
- W216
- W221
- W211

Package Contents
- 1pc × Mercedes-Benz AKL Adapter
- 1pc × J1K02_BENZ Wiring Harness
- 1pc × M821 Quick Guide
















































