Vagtacho (i think especially old versions) dont read complete range and only change two mileage strings. But there is another short checksum in other memory range. So if you dont change it too you will get 999999km result. If you didnt drive yet write back your backup and you will have old value. Driving 1km will not fix it! Anyway there is nothing really broken, it´s enough to change mileage with other good tool or read processor by direct connection and use mileage calculator. These M73 dont have external eeprom, you have to read MC68HC912DG128
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