Global Machinery Company Sierra 1999 - Manual (Page 304)

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Filling Your Tank (Gasoline Engine)
If your vehicle has a diesel engine, see “Filling Your
Tank (Diesel Engine)” in the Diesel Engine Supplement.
The fuel cap is located on the left side of your vehicle.
CAUTION:
Gasoline vapor is highly flammable. It burns
violently, and that can cause very bad injuries.
Don’t smoke if you’re near gasoline or refueling
your vehicle. Keep sparks, flames and smoking
materials away from gasoline.
While refueling, hang the filler cap by the tether using
the hook located on the inside of the filler door.