DIC MPG Glitch?

vancealot29 · November 18, 2019

Found an odd glitch (odd to me at least) this weekend. When I was looking at the 400 mile MPG on the DIC (as I was approaching 400 miles on my tank), I was seeing 22.1 MPG. When I scrolled up to the trip meter, those same 400 miles since my last fill up were showing 22.6 MPG. I would think a tenth or two falls into a margin of error, but a .5 difference seems large to me. The pictures were taken less than 30 seconds apart (within the same mile as you can see).

Do you think there are any other reasons it would be so off? I realize it is only 2% or 3%, but it just seems like a lot to me. There are probably a multitude of reasons why, but I would think that GM would have had these values synced some way.

Either way, not complaining at all with either 22.1 or 22.6, I just found the discrepancy interesting.

Chris Callanan · November 18, 2019

I would say the bigger problem is you taking pictures while you are driving

MaverickZ71 · November 18, 2019

If you want accurate miles per gallon, calculate it by hand. Some DIC's has been known to be overoptimistic. Some say the General wants everyone to feel warm and fuzzy that they are getting better fuel mileage than they are. Others say they calibrate each year for one transmission/rear gear/tire type and size for each engine and then put that in each truck off the line, so a High Country with highway tires and economy gear gets the same DIC calibration as a TrailBoss with off-road tires and a towing gear. Mine has been at least 7-10% overoptimistic on gallons used and MPG since new. And the dealer can't recalibrate it.

It's Tim · November 18, 2019

44 minutes ago, Chris Callanan said:

I would say the bigger problem is you taking pictures while you are driving

For some as yet unknown reason some don't see that as a problem, Darwins kids?

Could also just be a Floridain thing...

aseibel · November 18, 2019

I have yet to see anyone explain exactly how the DIC calculation works. It seems to take a bunch of instantaneous readings and average them. I don't believe it is actually measuring the total fuel burned and dividing by total miles driven, which would be the only accurate way.

Pretty much every discussion about the DIC fuel economy leads to an agreement that the DIC readings are too optimistic. In my experience they are fairly close, usually 0.25 - 0.5 mpg higher than hand calc. (which would mean its within 3%)

Short story, don't worry about the 0.5 difference between the screens. Hand calculate it if you really want to know your fuel economy long-term.