GMC Sierra 2008 Owner's Manual page 230

Trip Odometer
Press the trip/fuel button until TRIP displays. This
display shows the current distance traveled in either
miles (mi) or kilometers (km) since the last reset for the
trip odometer. Pressing the trip odometer reset stem
will also display the trip odometer.
The trip odometer can be reset to zero by pressing the
set/reset button while the trip odometer is displayed.
You can also reset the trip odometer while it is displayed
by pressing and holding the trip odometer reset stem.
The trip odometer has a feature called the retro-active
reset. This can be used to set the trip odometer to the
number of miles (kilometers) driven since the ignition was
last turned on. This can be used if the trip odometer is not
reset at the beginning of the trip.
To use the retro-active reset feature, press and hold
the set/reset button for at least four seconds. The trip
odometer will display the number of miles (mi) or
kilometers (km) driven since the ignition was last turned
on and the vehicle was moving. Once the vehicle begins
moving, the trip odometer will accumulate mileage. For
example, if the vehicle was driven 5 miles (8 km) before
it is started again, and then the retro-active reset feature
is activated, the display will show 5 miles (8 km). As the
vehicle begins moving, the display will then increase to
5.1 miles (8.2 km), 5.2 miles (8.4 km), etc.
3-60
Fuel Range
Press the trip/fuel button until FUEL RANGE displays.
This display shows the approximate number of
remaining miles (mi) or kilometers (km) the vehicle
can be driven without refueling. The display will
show LOW if the fuel level is low.
The fuel range estimate is based on an average of the
vehicle's fuel economy over recent driving history and the
amount of fuel remaining in the fuel tank. This estimate
will change if driving conditions change. For example, if
driving in traffic and making frequent stops, this display
may read one number, but if the vehicle is driven on a
freeway, the number may change even though the same
amount of fuel is in the fuel tank. This is because different
driving conditions produce different fuel economies.
Generally, freeway driving produces better fuel economy
than city driving. Fuel range cannot be reset.
Average Economy
Press the trip/fuel button until AVG ECONOMY displays.
This display shows the approximate average miles per
gallon (mpg) or liters per 100 kilometers (L/100 km).
This number is calculated based on the number of mpg
(L/100 km) recorded since the last time this menu item
was reset. To reset AVG ECONOMY, press and hold the
set/reset button.