1998 GMC Sonoma Owner's Manual - Page 257

When you put the cap back on, turn it to the right (clockwise) until you hear a clicking sound.Make sure you fully install the cap. The diagnosticsystem 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'' in the Index. Filling a Portable Fuel Container NOTICE: If you need a new cap, be sure to get the right type. Your dealer can get one for If you get you. the wrong type, it may not properly. This may fit cause your malfunction indicator lamp to light and your fuel tank and emissions system may be damaged. See "Malfunction Indicator Lamp" in the Index. Never fill a portable fuel containerwhile it isin your vehicle. Static electricity discharge from the container can ignite the gasoline vapor. You can be badly burned and your vehicle damaged if this you occurs. To help avoid injury to and others: Dispense gasoline only into approved containers. Do not fill a container w'hiIe it is inside a vehicle, in a vehicle's trunk, pickup bed or on any surface other than the ground. Bring the fill nozzle in contact with the inside of the fill opening beforeoperating the nozzle. Contact should be maintained until the filling is complete. 0 Don't smoke while pumping gasoline. 6-7