2000 Mercury Mystique Owner's Manual - Page 200

Maintenance and care Cleaner air Ford approves the use of gasolines to improve air quality, including reformulated gasolines that contain oxygenates such as a maximum of 10% ethanol or 15% MTBE. There should be no more than 5% methanol with cosolvents and additives to protect the fuel system. Fuel filler cap If the check engine indicator comes on and stays on when you start the engine, the fuel filler cap may not be properly installed. Turn off the engine, remove the fuel filler cap and reinstall it being careful to align the cap properly. If you must replace the fuel filler cap, replace it with an authorized Motorcraft part. The customer warranty may be void for any damage to the fuel tank or fuel system if an authorized Motorcraft fuel filler cap is not used. The fuel system may be under pressure. If the fuel filler cap is venting vapor or if you hear a hissing sound, wait until it stops before completely removing the fuel filler cap. Otherwise fuel may spray out and injure you or others. 200