2010 Toyota Prius FCD Inaccuracy

WoW!.. you were moving right along!
You have a good radar detector?

 

Didn't need one, I set the cruise control for 3 MPH over the speed limit because my speedometer is about 2 MPH fast. But the speed limit where I was (Idaho, Utah, Arizona, and Nevada) is 75 on the freeway and 65 on other highways except Nevada which is 70 on other highways. I didn't go through any big cities so I didn't spend any time siting at stop lights or in traffic. My last 450 miles were mostly in Oregon, non-freeway, speed limit 55 and my mileage for that tank was 54 MPG, but I went down about 4000 feet during that leg also which certainly helps.

Also took a few side trips. Went up Wheeler Peak in Great Basin Natl Park which is about 16 miles of 8% grade. When I went up there in the Gen2 the battery was down to two bars within the first couple of miles and it just went the rest of the way up on the ICE. This car (my Gen3) did get down to two bars a time or two on the way up but then managed to recharge itself and arrived at the top with 5 bars in the battery. When I started up the SOC was 6 bars with both Gen2 and Gen3.

Found one place on Oregon Highway 205 just out of French Glen that has a 14% grade for a couple of miles, I didn't even know they made highways that steep.

 

Many ways, like a service bulletin etc. Often time the "fixes" aren't applied unless a complaint is made.
But if Ken @ Japan is right , and I suspect he is, then nothing broken, and you don't fix something that's not broken.

 

Any more word on this?

One thing I noticed that might be coincidence, but maybe not... For the first time I didn't refill until a little after the almost-empty beep. (I usually fill up around 1/4 to 1/3 tank indicated on the fuel gauge.) And my calculated mileage was the farthest off that it's ever been from the indicated mileage: about 5.7% too high.

I've seen suggestions that it's intentionally 5% high, though every tank until this one has been well below that. I've seen discussions that perhaps there's a long-term issue and someone needs to do an experiment where they compare daily indicated readings to long-term indicated readings to see if there's some kind of accumulated, per-trip error. But has anyone thought that it might be related to something that happens when the tank is run lower?

 

Well I had my Prius Tech call Toyota tech help in Torrence to get a fix. The answer is there is no problem and they never heard of the problem before. So another call to Toyota customer care tomorrow.

Wayne

 

I just checked mine today. This was the first time I have compared the calculated gas mileage to the HSI display. It was off 1 mpg at the first click of fuel nozzle and rounding up to the next 25 cents.
The display said 53.0 mpg and actual calculating came out to 51.98 mpg. Close enough to keep me happy. It would have been at least 2 mpg higher but the cooler weather in the last week or so is killing my gas mileage.

 

Not sure if this happens in the US - but in India, I was working with one of their largest refineries/gas station outlets. They intentionally run 91 octane in the lower grade pumps. From what I understand, there is no difference in cost, but customer perception means a lot (of course they run many 2 stroke engines - where you will easily see a difference).

 

After a little over 10,000 miles mine is averaging 4% optimistic. It has been as high as 12% optimistic and as low as 0% but usually between 3 and 5%. My 2005 average just a fraction of a percentage optimistic. It was so accurate that after 20,000 miles or so I stop calculating. Becuase of the bladder it was much more accurate on a single tank than the calculated.

 

After 3000 miles and 7 tank refills, I am averaging 3.6 mpg error between displayed versus calculate. This is a 7.6% error.

 

Mine has been off alot too.
About 5 to 12%

Can;t wait for a fix.

It seems to me the discrepency is more prevelant in the Package V cars?

 

no bladder on the G3.

 

Wayne,

Did you ever gt any more info from Toyota about this? I've been e-mailing them and been told multiple times that the MID MPG display is an estimate they do not see this as a problem. Their responses are at the end of this post.

How about anyone else? I know some people have contacted them, but I'm thinking that we need to swamp them with requests to correct this problem.

10:28/09:
The electronic read-out of the miles per gallon is an electronic extrapolation based on various inputs such as throttle position, engine load, vehicle speed, and engine speed. It is not an exact measurement of real-world fuel efficiency.

10/29/09:
We appreciate your concern and respect your investment in ensuring accurate MPG readings. To recapitulate to your initial inquiry, we are not aware of any anomalies with the electronic MPG gauges, and do not reflect any Special Service Campaigns, bulletins, or recalls related to this issue. As such, se are similarly not aware of any pending corrections or modifications to the systems.

11/11/09:
As previously advised, your Prius will calculate miles per gallon achieved as an estimate. It is not exacting.

 

I would think these answer would end all discussion
It is an estimate.
And beside that all gas pumps will have a +/- on how accurate the pump is, also the temperture will change the volume of the gas

 

That's a pretty lame excuse set. There is no reason for the ECU control measurement to be so inexact and all in the same direction...other than intentionally misleading the driver into believing he/she is getting better mileage than he/she is actually getting.

My GenII's departure is presently 0.55% optimistic after 14,000 miles. There is no really good excuse for the GenIII error to be 10 times greater than that.

 

If the tank is underground, isn't the temp pretty much stable? That would pretty much void any discernible volume difference, wouldn't it?

 

I have to agree with Shawn on this one. Granted, the fuel calculation is just an estimate, but if that were the cause of the discrepancy, we should be seeing values above and below the actual computed mileage. Having the error always in the same direction suggests a deliberate bias in the calculation.

I will also grant that the gas pumps are not 100% accurate, and certainly there is an incentive for them to be biased on the low side. This could account for some of the error, but inspections of gas station pumps show the normal error to be much less than that of the Prius fuel computer on the Gen IIIs.

Tom

 

i fail to understand Toyota's apparent non-response to this issue. its simply a software programming issue. is it they are unable to fix it?

have other priorities right now? i dont get it. to be honest with you, i fully expected a letter or email advising of a flash upgrade...ya know, take to dealer, sit for 90 minutes, try to look like you are not completely bored out of your mind kind of thing

its almost like dealing with Microsoft. microsoft has a great way of taking forever to address major security issues then acting like their building is on fire when they finally release a fix 3 months after the fact... also 3 months after every hack site in the world has posted the vulnerability.

 

You can calculate your mpg by dividing the number of miles you have drive by the gallons of gas you put in your tank from the last refill.

Otherwise you might try reading the whole ten pages of posts in this thread again.

I dont think toyota is going to be sending you any letters about your FCD accuracy.

 

I doubt that flippant approach will work for long. Eventually someone will sue Toyota for fraud because of the magnitude of the error and its direction. And eventually the press will crucify them for it as well. This whole FCD inaccuracy problem reeks of dishonest marketing practices. All we need to complete the picture is some greasy used car salesman with a cheap hairpiece and bright, mismatched polyester suit.

 

Well if there was a conscious decision to be deceptive, I can't imagine they thought we wouldn't figure it out.
That alone would be a stupid underestimation of the common buyer.... most people who buy the Prius will have gas mileage in mind.....

All it takes is one person to let the cat out of the bag.

Priuschat is filled with members to check the numbers and many are tied to the press.