This guide provides a detailed, expert-level walkthrough for manually replacing the Individual Serial Number (ISN) in modern Bosch MG1 and MD1 ECUs by editing the EEPROM dump. This procedure is essential when swapping a vehicle's engine control unit (DME) with a used or donor unit.

Disclaimer: This is a high-risk procedure intended for advanced automotive technicians only. Incorrectly editing an EEPROM file can permanently damage ("brick") the ECU. Always create multiple backups of your original files before making any changes. Proceed at your own risk.

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Required Tools & Files

• An EEPROM programmer capable of reading and writing the specific memory chip in your MG1/MD1 ECU.
• A professional Hex Editor software (e.g., HxD, WinHex).
• The EEPROM dump from the ORIGINAL (ORI) ECU. This is the most critical file.
• The EEPROM dump from the USED/DONOR (USED) ECU. This is the file you will modify.

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Phase 1: Understanding the ISN Data Structure in MG1/MD1

Before you begin, you must understand how to identify the ISN data within the EEPROM dump.

1. ISN Composition: The full ISN is composed of two main parts, often highlighted in different colors in analysis software:

• EGS ISN (Blue): The security data related to the gearbox controller.
• DME ISN (Red): The security data for the engine controller itself.

2. The ISN Block Pattern: The crucial data block you need to transfer is a **32-BYTE** sequence (16 bytes + 16 bytes). The key characteristic of this block is that it is **repeated twice** within the EEPROM file.

3. How to Visually Detect the ISN:

• Open the EEPROM dump in a hex editor.
• Look for two identical blocks of 32 bytes (which appear as 2 lines of 16 bytes each in most hex editors).
• These blocks are typically separated by several other lines of data.
• Ignore any blocks that are filled with `00 00 00...` or `FF FF FF...` as these are empty or unwritten areas. The ISN block will contain complex, varied hexadecimal values.

Special Mention: While the logic is similar across MG1/MD1 ECUs, there can be slight variations. If you have difficulty locating the ISN visually, it is recommended to use "2nd hand programs" or specialized ISN detection software to help you identify the correct data block first. These tools may have different algorithms to try, as shown below.

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Phase 2: The Step-by-Step ISN Transfer Procedure

Step 1: Read Both EEPROMs

• Carefully read the full EEPROM data from both the original ECU and the used/donor ECU. Save them as separate files (e.g., `ORI.bin` and `USED.bin`).

Step 2: Locate the ISN in the ORIGINAL Dump

• Open `ORI.bin` in your hex editor. Visually scan the file and identify the repeating 32-byte ISN block as described in Phase 1. This is the data you need to copy.

Step 3: Locate the ISN in the USED Dump

• Open `USED.bin` in your hex editor. Find the corresponding 32-byte ISN block in this file. This is the data block you will overwrite.

Step 4: Perform the ISN Swap

• This is the most critical step. Carefully select the entire repeating ISN data block (both 32-byte parts) from the `ORI.bin` file.
• Copy this data.
• Go to the `USED.bin` file and overwrite the existing ISN data block with the data you just copied from the original file.
• Pro Tip: Be extremely careful with spacing and alignment. Some cases may require you to copy an extra line of data "up-down" to ensure full compatibility. Look carefully at the surrounding data structure. Do not make "crazy" movements or assumptions.

Step 5: Save & Write Back

• Save the modified `USED.bin` file. It's recommended to save it under a new name, like `USED_mod.bin`, keeping the original as a backup.
• Write the modified EEPROM data back to the used/donor ECU using your programmer.

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Phase 3: Finalization in the Vehicle

1. Install the modified donor ECU back into the vehicle.
2. Connect with E-Sys and perform a "reflash" (update software) and "coding" on the ECU.
3. Clear any fault codes. The vehicle should now start and run correctly with the adapted ECU.

Job DONE! Congratulations, you have successfully replaced the ISN.