Overview

Checksums exist to verify the integrity of data and ensure the data has not changed. Your car's engine management system uses checksums to protect the engine components in the event the data on the ECU were to be corrupted or changed accidentally.

Checksums are embedded in the ECU file. The same model ECU will have the same checksum values, because the code on the ECU is the same. They are calculated using data in the file. The ECU contains a few different checksums, depending on the ECU model.

The ECU will recalculate some checksums every startup and compare the values to the one stored in the ECU. If they do not match the stored checksums it assumes data has been corrupted and will not allow the engine to start to prevent possible damage or other annoying things.

When you modify the ECU file you absolutely should recalculate the checksum values. This would be tedious if done by hand but fortunately for us MTX-Electronics has released a $15 checksum plugin for TunerPro that makes this process seamless.

ECU Specific Data

B5 S4 8D0907551M (M-box) ECU

Checksum value locations:

• 0x08038 - 0x0803F
• 0x1B9B0 - 0x1B9B3
• 0x1FBB2 - 0x1FFD1
• 0x7A866 - 0x7A875
• 0xFFFE0 - 0xFFFE7

Utilities

• MTX-Electronics' $15 checksum plugin for TunerPro - The most popular method used in the Nefmoto community
• Andy Whittaker's ECUFix
• ME7Check is a free executable written by forum member setzi62 will tell you whether the checksums in a file are valid or not. It does not correct them but is sometimes useful.

Resources

• Wikipedia Checksum article
• Andy Whittaker's excellent breakdown of checkums in ME7