The gas mileage readout in My 2005 HAH nav system seems flaky in a couple of respects...

a) On a leisurely drive down the Sacramento River Road at about 45 mph I was averaging 37 mpg pretty for quite a few miles. Then all at once the mpg dropped to 31. Then continuing on at 45 mph it gradually increased. Huh??

b) I dont' expect the MPG in the Navi and the driver's console to match precisely, but sometimes they differ dramatically. If the first hundred miles or so on a tank of gas are around town (thus lower mpg) the variance is especially great. It's been said that a man with two wrist watches never knows what time it is. I resemble that. Which "watch" is better?

Alan

 

I don't recall where each unit gets their signals from, but I do remember they're different. In fact, I think there's a thread on this forum that discusses it. Perhaps, try doing a search under the HAH section.

It seems like the dash readout is the most accurate. I try to use the same fuel pump for filling up and I do my calculations by hand. Mileage divided by gallons. My dash readout is always the closest. The FCD in the Navi always seems to read high.

 

I don't have the NAV option, (totaly pointless here in Wyoming), but the dash mpg meter is consistently high by about 1mpg. This may be related to altitude here in the rocky mountain region. The only tank that measured, by calculation, greater than the dash meter was on a single trip in elevations mainly below 3000ft.