2010 Toyota Prius FCD Inaccuracy

Speed calibration is not related to odometer calibration. Because of legal requirements, most automobiles are calibrated with optimistic speedometers. On the other hand, odometers are required to be fairly accurate. Of course, after market wheels and tires can change the calibration.

Tom

 

66mph

 

Have the Scangauge gurus come up with a way to put in a correction factor in the 2010 Prius FCD calculation like this can be done with the Scangauge calculation?

 

That's what I want. It would be even better to have a correction factor that can be changed like with the Scangauge.

 

I imagine that Toyota would take the position that the FDC is intended to monitor relative fuel economy, rather than representing actual MPG. I haven't read all of the fineprint, but I bet there is some statement to this effect.

 

Do we have any objective evidence that the odometer is not wrong as a result? Or are we just taking the manufacturer's word here?

This is what I tend to observe (approximation) with my (winter mode) stock wheels with Nokian snow tires at 38psi all around:

GPS = Speedometer
50mph = 50 mph
65mph = 63/4 mph
72mph = ~70 mph
85 mph = ~82 mph

 

I agree with you. If the display is not going to be close to accurate why have it? I serves no purpose. I can look at mine and subtract 5 MPG and come real close to the calculated value. If your going to do something, do it right.

 

There're too many variables affecting the real consumption calculations here.
1. fuel pump accuracy, (for example, I consistantly topped up my Civic to 35 litres at a particular pump, but the Civic has a max fuel tank of 33 litres! No matter how many times I complaint, they just promise to look into it but it was the same a few years later. Of course I never go back there to fuel anymore.) I don't quite trust government regulated calibrations of the fuel pumps. If anyone who should be sued for fraud, it should be the big oil companies, (and of course we'll all loose.)
2. fuel temperature,
3. the type of fuel you use,
4. the low fuel level point where you think you've used up the gas down to the same level when you last fill it up: How do you determine what's left in the tank? I don't suppose you drive it untill you use up the fumes in order to know it's really empty!

If you rely on the flashing signal to indicate low fuel, how do you know if it's always flashing at the same level. Is it possible that this level could be a variable thus affecting your real fuel consumption calculations? Is it possible that it flashes earlier/later due to the inclination of your car at that moment? Does temperature affects it too? How far do you have to drive to fill'er up after it started flashing?

I think an average error of 5% is very acceptably low considering part of the error may come from your own measurements/calculations caused by so many factors.

Even the police would not charge you if you drive over the speed limit by 5%.

 

I'm only on the second tank in my Prius, so I don't have much data yet, but my experience with other cars with fuel consumption displays is that they have read 5-10% high. I'm sure this is deliberate, if a little "unethical," but that's the way they are. The Chevy Malibu Maxx I traded on my Prius read high, as does my Mini Cooper.

 

My average mpg readout is around 5% over actual and my speedometer is reading 10% over actual. Surely on a car with factory fitted Nav, which uses GPS, the speedometer should be more accurate. Would a tyre re-calibration on the Nav make things better, this is a 3 month old car with 1700 miles on it (and the tyres) ?

 

Your part of the world requires the speedometer to read high. Blame your politicians.

Tom

 

I have to agree. Yeah my mileage also reads hiGh as shown in my signature but my speedometer is very accurate. I have never seen More than 1 mile per hour difference When measured by gps or the varius radar signs that has displays showing your speed

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