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Is there a way to understand the ECU files hex changes applied by the software? I'm new to ECU files and struggling to understand possible areas of interest in the file.

For example, when the language change operation was performed on Prius (through software), following changes were observed:

enter image description here

Now I'm interested in understanding this change. i.e,

  1. How could software know this specific offset is the place to make change?
  2. How did software calculate new values to replace the old ones?

After some research since a week, what I already came to know is that there are maps defined in files. But I couldn't find any well documented structure of the files explained anywhere. This is where i'm stuck for long.

Can someone please explain, how can I identify this language change potential area, so that I can try it myself in other car? I have to do it on other car as well, so I'm interested in doing myself. I'm already a programmer, but new to ECU and mechanical stuff. Any help / guideline will be appreciated.

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  • Off topic here, but try converting the hex codes...
    – Solar Mike
    Jan 16, 2021 at 14:49
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    If you are already a programmer, you should know that can only be answered by reference to tables, or by reverse-engineering. You can't tell much from a hex dump not even how many bytes for each function. For example, there could be four bytes to control the language, two of which have a shared value between the old and the new langauge. Some of the changed values might be a consequence of setting the language, you show 2 pairs have changed. Perhaps you can find a hacker's guide. Jan 16, 2021 at 15:27
  • @SolarMike, converting hex codes to what? can you please explain a bit. Also, what should be the correct place for this discussion? as you pointed out that it's off topic here. Sorry about that.
    – Zeeshan
    Jan 18, 2021 at 9:39
  • @WeatherVane, Thanks for the pointing this out. I have got you, and in fact, as mentioned in question as well, the reference table / guide is what I'm unable to find. There isn't any well documented guide on this.
    – Zeeshan
    Jan 18, 2021 at 9:41

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