And regarding assuming anything is linear, I don't know. For the BMW, it is a programmed mapping that is probably piecewise linear, but who knows how many segments Honda used, or even if they use a similar approach.
I just tend to be skeptical and careful about believing things - could be true. Maybe even probably close to true, but safer to count on what you know.
As far as why Honda does it, the consensus for BMW's is the same as CroMath says:But if this is all true, as I expect it is, it is actually another reason to not be so concerned with the temp gauge. Not to rely on it, either way."My guess is that dealers don't want to waste their time and burn up their reputations in front of ill-informed clients by refusing to fix non-existent problems with the temperature gauge that are really harmless fluctuations within the normal range. The downside, of course, is that people who actually have the knowledge and ability to interpret the information properly are by default not trusted to receive it."
If S-VCM can do what it says it does, maybe it could actually adjust the signal to amplify the overheating signal when it is detected. I think the better way would be to deal with the gauge separately from the ECM, but since it's already right there, detecting temp and adjusting itself when it detects an overheated condition, it could perhaps also then de-map the condensed Honda gauge mapping.