GMC 2007 Sierra 1500 Pickup Owner's Manual page 476

When replacing the fuel cap, turn it clockwise until it
clicks. It will require more effort to turn the fuel cap
on the last turn as you tighten it. Make sure the
cap is fully installed. The diagnostic system can
determine if the fuel cap has been left off or
improperly installed. This would allow fuel to
evaporate into the atmosphere. See Malfunction
Indicator Lamp on page 258.
The TIGHTEN FUEL CAP message will be
displayed on the Driver Information Center (DIC) if
the fuel cap is not properly installed. See DIC
Warnings and Messages on page 270 for more
information.
476
CAUTION:
{
If a fire starts while you are refueling, do
not remove the nozzle. Shut off the flow
of fuel by shutting off the pump or by
notifying the station attendant. Leave the
area immediately.
Notice: If you need a new fuel cap, be sure to
get the right type. Your dealer can get one
for you. If you get the wrong type, it may not
fit properly. This may cause your malfunction
indicator lamp to light and may damage
your fuel tank and emissions system. See
Malfunction Indicator Lamp on page 258.