Checksum is one of the most important technical aspects of ECU file modification. When data inside an ECU file is changed, some ECUs require the checksum to be recalculated. If the checksum is incorrect, the ECU may reject the file or behave unexpectedly. For this reason, professional ECU file processing involves more than simply changing calibration data. The ECU's checksum structure must also be taken into account. Checksum calculation is absolutely essential, especially with devices like KT200, Foxflash, and Kess V2, as well as all devices that lack checksum support.
Sometimes you may need to send both the original and the modified files. To speed up the process, you can zip both files together and send them at the same time; it makes no difference whether you use Zip or Rar.