The Check Fuel Cap Indicator
WARNING: This page is about a different car, the 2003 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.
The check fuel cap indicator is used to indicate significant leaks in the fuel tank evaporative system due to loose fuel cap. Fuel tank pressure is monitored by the PCM. If a leak is detected, it signals a fault to the instrument cluster via the SCP network. Once the PCM has detected a loose fuel cap and the check fuel cap indicator is illuminated, the check fuel cap indicator will remain illuminated until the fuel cap is secured and the vehicle has been running for several minutes.