This has been mentioned in a couple other related threads but I didn't see a dedicated thread about this TSB. Sorry if this is a duplicate.

Honda released Service Bulletin 09-086 on November 18, 2009 for a software update that will correct the 10-15% error (reads higher than actual mpg) that many 09's have when calculating the mpg via the trip computer. It sounds like owners who've had it done are now seeing readings within 2-3% of the hand-calculated mileage.

A copy of the TSB can be found here for the time being...

Fit MPG

 

Is there any possibility that we could update this ourselves without having to go to the dealer?

 

Sure can. You just need to build or buy the device they use to flash the ECU. Then, get your paws on the image. Let us know how you fare.

 

Thanks txmatt. Anyone know of any other TSB's for the GE8? Need a thread for those.

 

Why still 2-3% of manual calculating? Shouldn't Honda get it right?

 

my dealer in montreal canada who took my vin# didn't know this....maybe its still in the us only?

 

My gauge was about 10% optimistic on the first, and every tank thereafter. Since the update last week, I don't have enough data to be accurate (due to the vagaries of filling a Fit gas tank), but it seems to be within +- 0.5%. I've set up a spreadsheet to record not only each individual tank, but also to do a cumulative calculation on measured vs reported MPG. By June or so I should have good data.

 

For one, there's error in manual calculating unless you're filling up to the neck or some other point that you know is 100% repeatable from fill to fill.

And I'm not so sure that the computer knows exactly how much fuel is dosed by every injector squirt. Is that exactly the same every single pulse? While the injector may be assumed to be either on or off, there's probably a tiny ramp up and ramp down to full flow on each pulse such that it's not simply a constant flow rate * duty cycle calculation. And that behavior may change over the life of the injector.

Assume one tank of gas gets you 300 miles at 60 mph and ~3000 RPM. That would take 300 minutes at 3000 RPM so you've got 900,000 squirts of each injector over that tank of gas. Lots of opportunities for small errors to show up. Plus tire diameter changes with tire pressure/temperature and tire wear which introduces small error in distance calculations.

And the display only has 1 decimal place to work with so anything between 34.95 and 35.05 may display as 35.0. There's 0.3% error in that range.

There's just too many variables to expect it to be exact. Certainly 10-15% is unacceptable. So what is "good enough" for a reading that most people pay only passing attention to? I agree that the more accurate the better, but a 2-3% error is going to usually be within 1 mpg which I think most folk would think is acceptable.

 

I'm going to wait for the software update that leaves the trip computer alone but increases the mpg to match the computer.

Cheers.

 

I don't think any valid conclusions about the accuracy of the new calibration can be drawn in less than a thousand miles of record keeping, preferably more. My gauge has reported both above and below what I have calculated since the software upgrade, whereas before upgrade it was always wildly optimistic.

 

Is there an update for the 2010 models, or is this apply to the '09 only?

 

Thanks for posting this. I'll need to have this done at my next oil change.

 

I would bet that Honda already updated the 2010's for this before they hit the showrooms.

 

Dang, if they come out with that I'm going to be really jealous that my GD doesn't have a trip computer.

 

since the fix i filled the tank twice.

first fill up...
car computer 31.3 mpg.
hand calculated 30.7 mpg.

2nd fill up....
car computer 30.8 mpg.
hand calculated 30.3 mpg

 

Great information, Thanks for taking the time and posting. Leif

 

The fix works. Print a copy and take it to your Honda dealer when making a service appointment. They may want to know if you really have the problem, so be prepared to discuss calculated vs reported gas mileage. This should take about an hour, and be covered under warranty.

 

I'd say call your service center first... if they know nothing about it, e-mail them the PDF file. this way you don't have to take the car "back" just for the TSB.

~SB

 

There will always be some error since tank fills will vary somewhat depending on when the nozzle "kicks off". This will vary from pump to pump depending on delivery pressure and other factors. With a tank as small as the Fits, +/- a quart or so variation on a fill-up can easily introduce a 2-3% error. this is why even calculated mileage can be off, and should be averaged over several tankfuls to be considered accurate. It just may be that the mileage meter is MORE accurate than my hand calculations now. I'll let you know when I've run a few more thousand miles since the fix.

If you are in a habit of "topping off" your fill-ups, to try to get more accurate calculations, you should stop. Overfilling the fuel system can damage the evaporative emissions control system, and repairing it can be expensive (don't ask how I know this).

 

I was kinda hoping that the update would do that. I'd like to be getting an HONEST 45 MPG.