For those of you that already drive Fits, how accurate is the computer on estimating mileage per gallon? My Cobalt computer and 2012 Express is always accurate within about a 1/2mpg, my dodge not so much! Often it is off 4-5mpg!

 

It's generally a couple mpg higher than my UltraGauge, but not badly.

 

When the 2009 fits were delivered, they were about 10% optimistic in reported fuel economy. There was a dealer flash made that improved them. After that flash I find that mine is still about 2-3% optimistic. When it reads 36 MPG, I am actually getting 35 MPG based on calculations.

Interestingly, my CRZ is more accurate and is always within 1% of my calculated fuel economy. Sometimes higher sometimes lower, but usually pretty darn close.

 

I never got mine fixed. It's 12% high. I use a calibrated Scangauge so I don't care.

 

Is the scan gauge usually right on?

 

Well yeah, the poster calibrated it.

 

Not necessarily, if the system is not consistent in its measurement of fuel, there could be inherent variation in the system.

 

The Scangauge reads straight from the OBD-II port. I assume the OEM gauge reads similar source information. However, the SG doesn't read anything from the onboard gauge, but does its own calculations in parallel to the onboard one.

If your driving style is consistent, it is right on. I do mainly suburban driving. As long as I stay there it's right on. I mean, averaged over a few months, it's within a couple tenths of a gallon. Any individual tank will be off, because the gas pumps are wildly variable. If I take a highway trip it'll be a few percent off, but still much closer than the built-in gauge.

 

Gas pumps are actually quite accurate, as they are regularly checked by whatever weights and measures department has jurisdiction.

What does vary is the amount of gas you can get into the tank and driving conditions. A slight slant in the way the car is parked might make a half-gallon difference in the fill. A 30 mile drive with a 15MPH headwind might change the MPG considerably.

Odometers are actually designed to be slightly pessimistic and speedometers optimistic, since manufacturers realize that there will always be inaccuracies and they don't want to be sued for shorting people on warranties or for their customers getting speeding tickets. My Scion, with stock 185-60R15 tires had a speedometer that read 4% high and an odometer that read 4% low. I replaced the tires with 195-65R15s and my speedometer is now perfect, but the odometer now reads about 8-9% low. I have to take this into account when calculating fuel mileage.

The instantaneous MPG indicators use the injector pulse width information to calculate the rate of fuel use and the speed information from the speed sensor. Dividing miles per hour by gallons per hour gives miles per gallon after a bit of averaging to smooth it out. It isn't super-accurate, but it is a good indication of how economical your driving is.

 

Yes, I'm sure that's what he meant.

 

Yep. That's why I'm averaging it and not relying on a single fill.

My other car, an 04 Odyssey, was part of the class-action suit related to the odometers. It read about 4% more miles than actual. I've verified that on the interstate. Pass by 10 mile markers and the van's odometer reads 9.6 mi. That made the warranty run out early, hence the suit.

 

Are you sure? If 10 actual miles were 9.6 odometer miles your warranty would run longer!

I'll bet that 10 actual miles were 10.4 miles on your odometer!

 

ah, right. Had a moment of dumb right there.

 

New member here.

Saw your threads. Anyone experiencing a wildly fluctuating average MPG reading on their 2013 Fit. Fluctuates between fills from 28 to 48 mpg. This is recent. Prior to May, readings were in the 35-38 range. Car only 4 months old! ! Dealer says "Duh".

 

Here is the only thing I could add for you. Whenever you reset your trip odometer, the fuel economy readout resets. If you reset your trip odometer and then start driving on the highway, there is a good chance, you might see 48MPG for several miles of driving at a speed of less than 60 MPH. Then if you reset your trip odometer and immediately drove around town, or in heavy traffic, your fuel economy might read 28 mpg or less. If you never reset you trip odometer, then the fuel economy will not show much variation, as it will be averaging allot of miles together.

 

Higher mpg is prety delicate and it doesn't take much to throw it off. I'd think your mileage is actually varying before I'd think your instruments are wrong.

 

Thats exactly how it works on all my vehicles. Best to not reset and you will eventually get a more accurate average reading.

 

Thanks for replies. I hope it is as a few of you have suggested. But a little more detail. My last drive on the highway, never got less that 48 mpg. I thought I was good, but never that good. At the dealer, the mechanic disconnected the battery, reconnected,drove out of the shop and immediately got 45 mpg ! ! ! He said it was squirrely, but had no answer. Dealer documented the event and continues looking for a (recent) Tech Bulletin. I can easily check mileage the old fashion way, and the meter is a better indicator of driving style, but my concerns: mpg reading consistently ultra high may affect the oil life % calculator??; and IF there is a faulty chip(?), what else by be misadjusted accordingly.

 

It's not accurate the first mile or two you drive because the odometer works in tenths of a mile. So there's a big difference between if it clicks a tenth just as you start to roll, or if it has to go a whole tenth before it sees a change in distance driven. Is that your issue?

 

Let it go for a whole tank and see if it looks more believable, then see how your next whole tank compares...