RI A6

I've been a bit interested in whether or not the on-board computer is accurate or not. As a result, I've been logging mileage and fuel consumption.

Recently, I returned from a 300 mile highway trip where I was able to stay on cruise control for almost the entire trip. I filled the tank at the start of the trip, reset the trip odometer, and reset the #1 average MPG in the on-board computer. With a GPS, I've determined that the speed that the computer displays is 1-2 mph faster than actual speed, at 70 mph. Or a little bit less than 2% error on the high side.

At the end of the trip, the computed MPG was 29.7 mpg. After filling the tank, the actual mileage, was 27.33 mpg.

Conclusion ... the computer is about 8.7% high in calculating fuel mileage, probably due to imprecise fuel metering.

I think this might be why some people are reporting 30 and 31 mpg with the 3.2 engine. I think it's possible that the computer is reading this, but the actual fuel mileage is probably lower.

kkemp

I know it was on the previous (C5) A6, see no reason why it would not be so on the C6. Making the adjustment on the C5 required a VAG-COM or trip to the dealer.

sinpolio

I believe that you have overlooked some important factors in your experiment:

Filling up your tank is a key element for your tests. As there is a large margin of error at the gas pump and its fuel cut off from one pump to the next, I believe the only way to make an accurate measurement would be to have gone to the same exact pump and for example set it to fill up to the point where it stopped, and not to fill up any more manually, etc...

JackKrash

I may just be confused.

pierreb

see my sig for a tire calc for adjustment.

RI A6

it was within 5 miles of the odometer out of 306. I'd say that's pretty darn close. That's a 2% error, not an 8.5% error, like the fuel mileage

RI A6

I'm very careful about the way I fill the tank, but that is quite possible. I'll continue to monitor with the same pump and report the results. However, I believe the computer is programmed to overestimate the fuel mileage.

ACSGP

and if there's a change, the computer may have to be re-calibrated.

My 2 cents.

RI A6

Don't the rest of you check your speedometers and fuel mileage?

As I've said, the computer speed is 2% fast, about 1.5 to 2 mph @ 70 mph. This is actually quite close. Speedometers are usually calibrated to be fast.

2% error in speed and mileage does not equate to >8% error in fuel mileage. Either fuel delivery is being measured incorrectly, or the averaging algorithm is wrong.

vanGogh

Hi, I have done 23000+ km study with my 3.0 TDI, and the result is that the MMi shows ~8-10% less than actual. It surely depends on fuel pump pistol and placement into filler pipe, some pumps stops as much as 10 litres before actually being full. In winter time the air nozzle could be filled with ice, so the pump senses overpressure and stops (knock downwards to clean before start filling)

Not done yet, but it should be possible to adjust in 5 % steps at Instrument module #17, select adaptation (advanced functions), go to channel 3, Enter 105, 110, or 115 (stock is 100).
(no warranty, found this from internet...)