Volumetric Efficiency is a percentage of what fuel/air enters the combustion cylinder against that cylinders theoretical capacity.
This PID will give the best results if your vehicle supports both MAF and MAP sensors. If both are supported, will show a range typically from 40 to 100%.
For normally aspirated (non-turbo) vehicles that only provide a MAF sensor, this will also show a range from approximately 40-100%.
For turbocharged vehicles that only provide a MAF sensor output, this will read from 40% to well in excess of 100% (at full load, this can be near 200% or above depending on the type of engine).
Faulty adapters will affect the accuracy of this PID.