Archives

I started a new thread for the updates specifically for the issue of the inaccuracy of the FCD (fuel consumption display) on the 2010 Toyota Prius.

We have about 4500 miles on ours and on every tank the hand calculated mpg is off 3 to 7 mpg from what the FCD reads. My wife gets about 54 mpg on the FCD and her tanks are usually 4 to 5 mpg less calculated. Last week I had two 500 + mile fills and The first was 5.5mpg less and the second 7.1 mpg. This was with a FCD display of 62 mpg which included a lot of around town in Madison for Hybridfest Green Drive Expo. The second tank read 64.4 mpg and it was fully highway driving. It was off by 7.1 mpg.

5 to 10% is out of the box for error. I fill up at the same station, same pump, same number of clicks, and same direction each time with the exception of the fill in Madison last week of which I estimated slope to be the same at the station I filled at.

I stopped at the dealer and had them check it out to get a paper trail started. Nothing was found so I followed up with a call to start a claim with customer care the next day. They took my information and later that day, Heather from customer care called back. She gave me a file number to record to use if I called back. She was going to investigate and call me back this week.

Heather just called back and said she had talked to field service reps and engineers and they informed her they were aware of an accuracy issue of 8% to 10%. They were looking further into the issue and expected something would come out in the form of a TSB.

Once again I am impressed by the quality of Toyota's attention to their product.

Hopefully they resolve it -- that is a ridiculous margin of error.

Good for you, Mike. As I wrote on Facebook, this isn't the first one of these I've heard of, so I'm glad you're on top of it!

Great seeing you at HF GDE. Sorry about Juanita's; I owe you some great Mexican. Let me know next time you'll be up this way.

~Linda

Hi Mike;

I started a process with Toyota Canada last week as well, detailing the very same issue and I even directed them to my blog for additional details.
As per my observations, the margin of error appears to depend on series of factors mostly related to the MPG range we strive for, but regardless of the elements we can account for in addition to the ones we do not yet know about, Toyota should issue an FE recalibration asap before this becomes a bruiser issue.

Cheers;

MSantos

I could tell from the conversation that she had with the engineers that it was an issue that will be addressed. I asked her if I could quote her on a TSB forthcoming and she said yes.:D

Hi Mike:

___Thanks for starting this. When I saw the 6 mpg overage as calculated at the Prius-III preview launch, my parents first tank at 6.1 mpg over, the Chicago to NY on a single tank and back on the same with again, a 6 mpg overage per the FCD plus yours and Manuel's, Toyota should be fixing this.

___When my parents Prius-III goes in on the next go-around, I will make sure they place a complaint request in for theirs too.

___Good Luck

___Wayne

I'm guessing the inaccuracy comes from how the relatively low gallons per mile at this rate. Going from 60 mpg (1.67 gpm) to 65 (1.53 gpm) to 70 (1.43 gpm) is probably very hard to measure.

Not that it's a good excuse since Toyota should expect customers are looking for a higher degree of accuracy in the Prius III. After all, why else would people be buying?

I'm guessing the inaccuracy comes from how the relatively low gallons per mile at this rate. Going from 60 mpg (1.67 gpm) to 65 (1.53 gpm) to 70 (1.43 gpm) is probably very hard to measure.

Not that it's a good excuse since Toyota should expect customers are looking for a higher degree of accuracy in the Prius III. After all, why else would people be buying?

You mean 0.0167, 0.0153 and 0.0143gpm respectively I presume?

Regardless of the reported mpg on the FCD, the gen II accuracy rate was MUCH better. How did the calcs go so wrong when going to the new gen?

I'm showing 3.92% optimism on the part of my 2G over 50,000mi. If that's annoying, 10% would probably drive me nuts.

I remember reading that one tank calculated MPG is inaccurate on the Prius due to fuel tank design. Average it out over several tanks for better accuracy.

Lets hope they get it fixed quick.

The gen II tanks have a bladder in them that makes it difficult to fill accurately unless you're used to it. The 2010 tank does not have a bladder and fill the same as a conventional car.

I remember reading that one tank calculated MPG is inaccurate on the Prius due to fuel tank design. Average it out over several tanks for better accuracy.

After 1600 miles, my FCD error is 4% (4.3%, but the small sample size and use of different pumps don't justify sub-1% accuracy yet).

Does Toyota measure fuel use by some true volumetric measure (e.g. fuel injector pulses), or does it use ScanGauge-style estimates (e.g. measure or calculate airflow, and assume fuel use from a known air:fuel ratio)? If the later, ethanol and other oxygenates will produce an error, and unlike ScanGauge, Prius doesn't have a path for the user to calibrate the estimates.

my understanding is the old one was injector pulses, specifically #1 times 4=fuel used

Hi Kacey:

___Air-flow from my understanding. The SuperMid measures through pulses but the FCD is air-flow. I will check that out with some within Toyota but that one may take a while.

___In the end, the offset was "planned" and that is what makes it so hard to contemplate that a corporation would do such a thing :(

___Good Luck

___Wayne

Every Toyota I ever owned was overly optimistic with it's fuel consumption meter device. That is why I always use the hand calculated method. It seems like it would be easy for them to fix the problem though.

Hi Mike:

___My parents completed their second fill and the same again:


Filled Prius tank today = 448 miles at 51.8 mpg. The car readout said about 57 mpg, so there is the 6 discrepancy again.
___Blaster, the Prius-I had about a 5 mpg overage, the -II about a 2 mpg overage, the -II Touring was a lot closer to actual during the Chicago to NY stint for some reason last summer but the -III is showing a 6 mpg overage and that is just to high for anything other than a marketing scheme. All FCD's can be dialed in to within + or minus two percent and Toyota's continuous over estimates is not playing fair to the rest of the world and in particular to their owners.

___Good Luck

___Wayne

I just filled ours again. My wife drove this tank and here are the results:
4950 miles
487 miles @ 54.4 fcd
48.68 mpg calculated for a difference of 5.72 mpg or 10.625%

Mike, isn't that really 11.75% error (FCD/reality)?

Mike, isn't that really 11.75% error (FCD/reality)?

correct. thats ridiculous..I make better guesses using my fuel gauge and odo

OK, first fill up since Hybridfest. Indicated on the HSI was 800 miles and 73.8 MPG. Gas fill was 12.075 gallons for a calculated of 66.28 MPG. That would be a 10.2% error, way unacceptable. I've been driving on the blinking light for 43 miles, what if I wasn't on city streets with a gas station close at hand. BTW my ScanGage said 64.1 MPG, way better.

Wayne

Filled up for my wife today and the latest tally is:

429.9 miles
8.785 gallons
FCD 54.2 mpg
actual 48.94 mpg

Hi MIke:

___Same ol, same ol...

___Linda, did you read the Preview (http://www.cleanmpg.com/forums/showthread.php?p=196751#post196751)?

___Good Luck

___Wayne