Check Fuel Cap Warning Indicator
WARNING: This page is about a different car, the 2006 Mercury Milan, 2006 Lincoln Zephyr, and 2006 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
The PCM monitors pressure in the fuel evaporative system and detects critical losses of pressure. When a critical loss of pressure in the fuel evaporative system is detected, the PCM provides a message over the communication network and the instrument cluster illuminates the check fuel cap warning indicator.