2008 GMC Acadia Owner's Manual - Page 325

When replacing the fuel cap, turn it clockwise until it clicks. 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 3-50. If your vehicle has a Driver Information Center (DIC), the TIGHTEN GAS CAP message will be displayed if the fuel cap is not properly installed. {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 3-50. 5-11