Basically it's power divided by consumption (Actual Engine Torque * RPM / FuelFlow), scaled from 0 to 100.
There are 2 Efficiency charts:
- Percent Efficiency measure efficiency relative to the maximum observed value in the whole trip. It's charted alongside RPMs and SOC for easy analysis.
It can't be directly compared between different trips or cars
- Absolute Efficiency reports efficiency value unscaled.
This may be used to compare different trips from the same car.
Comparing efficiency between different cars may be done with caution:
- on Toyota HSD cars, "Actual Engine Torque (Nm)" is a custom PID collected by ECU, and thus may be considered an accurate value, as much as RPM and FuelFlow.
- on generic cars, "Actual engine % torque(%)", a generic Torque PID is used. This value is a percentual value, and it can't be directly compared with values collected from HSD PIDs
So comparing absolute Efficiency values from two different HSD cars makes sense, while comparing to non-hybrid cars does not.