I have previously noted that the Prius display of speed is about 1 mph higher than actual as measured by GPS and those ubiquitous street radar signs. However, the OBD-2 display using the Garmin Mechanic exactly agrees with the GPS. I wonder how this relates to the well known display mpg being 3mpg or so higher than actual measured by tank fill-ups.
The exaggerated MPG is a Toyota marketing scam, while the OBD-2 velocity and odometer readings are more valid.
Consensus from past discussions is that the speedometer reads a bit high for legal and industry standards reasons. No meter can be perfectly accurate in all units, and some jurisdictions prohibit any units from reading low, so as a group they must be biased high so that the lowest ones are still legal. (The internal ECU figure is fairly accurate, but the Prius adds a bit to the dashboard display.) It reads even higher in many foreign markets. But the odometer reading is fairly accurate. It cannot read high without rolling out the red carpet for class action lawyers, who already hit up two of my past brands for 'warranty fraud', extracting millions in fees for themselves and a 2% warranty extension for customers. (Neither of my covered cars exhibited the claimed odometer error.) Toyota is capable of showing a more accurate MPG reading. The Gen2 proved it. But there are no legal pressures forcing it.
Yes, the odometer is very accurate! Its interesting that the speedometer in my 2004 Highlander was very accurate and the odometer as well.
I agree with fuzzy1 my GenII was totally accurate with computed MPG and the two Gen3 I have/had is about av 5% over almost 3 year in my dead Gen3 .... Also there is an international standard by the UN (more specifically ECE ) which gurantees speed reading is ALWAYS higher than actual speed !!
Just went on a 45 mile trip through the lower Sierra foothills. Prius display said 66 mpg, OBD-2 said 63 mpg. Its pretty clear the Prius display reads high based on specific software programming.
