on Sunday 11 November 2007 01:25 pm, someone posing as Ed H. took a rock and
etched into the cave:
I don't know about those of you oil burners but I've found my DIC to be
quite accurate. I was very meticulous on my mileage for about the first ten
months of owning my Avalanche.
Now, after 13 months, I've slacked off.
Mine is a 2005 2500HD, not a 2006. For me, the gallons used reads a
gallon or 2 low over a full tank's usage. As a result, the mpg reads
1 to 1.5mpg high. I've gotten the impression that the gallons used
sensor has sloppy calibration. You may get lucky.
When I recently stepped up my tire size from 245/75 to 265/75 in my 2004
2500HD I did notice a few issues - the calculated MPG dropped by about
1.5mpg, the speedometer was now off by 3 mph at 70mph (Speedo reads 70, GPS
reads 73 where before they were both the same), and the indicated mileage
traveled dropped for the same distance. All to be expected when using larger
When I checked with my local dealer about reflashing the computer to accept
the new tire size the service advisor advised against going through the
trouble. Why? Well it seems that speedometer/mileage error that is
acceptable to GM can be as high as 4% from the factory and since my new
tires were around 3% different than the stock tires I was still within the
margin of error.
Wished I'd have know that sooner - I would have put the larger tires on
earlier and made the warranty last a little longer!
Cheers - Jonathan
My '06 Duramax Dually is off both ways. When driving solo the DIC will show
lower miles per gallon than actual and the gallons used will be greater than
actual. When towing it is just the opposite, the gallons used will be lower
than actual and the miles per gallon will be greater than actual.
The gallons used are rarely off by more than 1 gallon whether I am towing or
driving solo. A one gallon difference over 25-30 gallons is probably within
the acceptable error margin.
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