I was playing with VAGCOM last night on the fabia and found the mileage check in the applications section. It does say there is a 5% error or readings but I just wondered how much anyone elses is out by speedo reads says 99289m and ECU says 97722m. I tested my friends fabia (1.4Tdi) and her is only 80 miles out.

I'm not worried just interested in what difference other people have if anyone has actually checked. If it was the other way around and the ECU mileage was more I might be a little worried.

I'm thinking that its out due to running for 80% of its life on 17" wheels.

I was playing with VAGCOM last night on the fabia and found the mileage check in the applications section. It does say there is a 5% error or readings but I just wondered how much anyone elses is out by speedo reads says 99289m and ECU says 97722m. I tested my friends fabia (1.4Tdi) and her is only 80 miles out.

I'm not worried just interested in what difference other people have if anyone has actually checked. If it was the other way around and the ECU mileage was more I might be a little worried.

I'm thinking that its out due to running for 80% of its life on 17" wheels.

Mine is quite a long way out as well, but it's in km, not miles in the ECU. And like yours, mine is reading low ie. my car is over-clocked.

That difference is only about 1.6% so not a great amount. I can't see anyone bother to try knock 1500 miles off the clock.

17 inch wheel size would account for it spot on. Not worth bothering about at all.

17 inch wheel size would account for it spot on. Not worth bothering about at all.

So how does the ECU and Odometer change for different wheel diameters and tyre sizes? Both will measure wheel rotations and therefore calculates distance travelled.

Edited 4 October, 201015 yr by Jim H

One works it out as rolled distance, and the other by speed and time, they will never match and never do.

All speedos are set to over read slightly to ensure any error is always on the legal side of accurate allowing for the slight differences in rolling circumference caused by different wheel/tyre combinations and wear. As mentioned the ECU will calculate the figure based on a standard rolling circumference. If that figure is changed it shouldn't affect the difference between the ECU and the Odo because they will have both changed by the same %age.

17 inch wheel size would account for it spot on. Not worth bothering about at all.

thought as much not bothered about it just interested in the reason cheers MoggyTech

Even VAGCOM states there could be upto a 5% error.