Trip computers wrong?

[Outfitter17]

Has anyone had problems with their computers? My mileage is correct, but on my last couple of trips it says that I am averaging 22.1 mpg. when I divide it manually on a calculator I get around 19.5 mpg which make more sense.
Also when I fill up I can put in 30 gals and the computer says I only used approx. 27.

Do I need to take it to the shop to get reset or recalculated?

[Duramaster]

What year, make and model of truck are you driving? :confused:

[DmaxMaverick]

The use of any power programmer can cause the same result.

[JohnnyR]

I've got a 2005 GMC Duramax and mine has been 5% higher than actual mileage calculated since the day I got it.

[Hook_'em_Horns!]

Has anyone had problems with their computers? My mileage is correct, but on my last couple of trips it says that I am averaging 22.1 mpg. when I divide it manually on a calculator I get around 19.5 mpg which make more sense.
Also when I fill up I can put in 30 gals and the computer says I only used approx. 27.

Do I need to take it to the shop to get reset or recalculated?

I’ve noticed a correlation with inaccuracies as to where I purchase fuel.

At some places, pumping amounts are within a few tenths of the computer. Others are 1.5 to 2.5 gallons over the computer usage.

Repeatedly the over/under is the same at the same places. Now that fuel is this high, I could be being robbed for 6-7 dollars at a time.

This, after begging to buy, passing the required qualifications to become a customer, leaving multiple Credit Cards and numerous forms of ID’s and granted the right to go and pump my own fuel for $100 or more.:cool: