I think that's going to be your only bet, just because it's a 3 Bar MAP doesnt mean the PCM can see the whole range. There are hardcoded limits (like the 255kPa limit you found) that you cannot get around, the PCM will never be able to see it. If you HAVE to have it, you're going to need to scale everything and get creative on how to display everything. FWIW, I see this being a huge can of worms and would not suggest it, likely way more headache.