Diesel fuel filter can separate water from fuel. If water more than specified amount is detected by "fuel filter warning sensor" installed at the bottom of fuel filter, "Fuel warning lamp" on cluster turns ON. Especially for high pressure pump and injectors of common rail diesel engine water is fatal. because water causes poor lubrication and corrosion in such accurate devices, furthermore, it leads engine hesitation. In order to prevent this harsh condition to engine, "Water warning lamp" turns ON to let driver relief the gathered water from the filter and engine power generation is limited.