ME7 checksums explained

If you edit a Bosch ME7 / ME7.5 BIN and flash it back without fixing the checksums, the ECU will usually reject the file — or in the worst case, refuse to start. This guide explains what the checksum is, why it matters, and how Ecuno handles it for you on export.

What a checksum actually is

A checksum is a number computed from the contents of a region of the flash. The ECU stores the expected value and, at boot, recomputes it over the same region. If the two do not match, the ECU assumes the flash is corrupt.

ME7 files contain multiple checksum regions:

• A small number of top-level checksums that cover fixed address ranges.
• Program / map (RSA-style and additive) checks over the calibration area.

When you change even a single byte in a map, the additive checksum over that region no longer matches the stored value.

Why editing a map breaks it

Say you raise a value in KFMIOP by a few counts. That byte lives inside a region that a checksum covers. The stored checksum still reflects the old bytes, so:

stored_checksum   = 0x8A31   (computed over the stock bytes)
computed_at_boot  = 0x8A3F   (your edited bytes)
0x8A31 != 0x8A3F  ->  ECU rejects the flash

The fix is to recompute the checksum over the new bytes and write the corrected value back into the file before flashing.

How Ecuno handles it

Ecuno keeps your original stock file untouched and works on a copy. When you export, it:

1. Saves any pending edits into the working BIN.
2. Runs ME7 checksum correction over the recognised regions.
3. Streams you the corrected file, ready to flash.

If the file is not a recognised stock ME7 image — for example, a file whose checksum routine was already altered by another tool — Ecuno will tell you instead of writing a value it cannot verify. That is deliberate: a silently wrong checksum is worse than a visible warning.

Checksum correction is scoped to Bosch ME7 / ME7.5. Support for other ECU families is not guaranteed.

Key takeaways

• The checksum proves the flash is intact; editing a map invalidates it.
• You must correct it before flashing, or the ECU rejects the file.
• Ecuno corrects ME7 / ME7.5 checksums automatically on export and warns you when it cannot.

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