GMC Sierra Classic 2007 Owner's Manual page 472

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 256.
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 267 for more
information.
472
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/retailer 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 256.