Ford Windstar Owner's Manual page 30

Electronic Gauges
Fuel Gauge
The fuel gauge displays approximately how much fuel you have
in the fuel tank. The number of bars illuminated in the display
indicates fuel level. Your ignition must be in the ON position to
read the fuel gauge. Read the fuel level at the top bar that is lit.
When only one bar on the gauge is lit, the fuel pump symbol
on the gauge will flash to warn you of a low fuel level
condition.
If the fuel gauge displays only the top two bars and bottom two
bars, or if the Distance to Empty function in the fuel computer
displays CO or CS, you must have the fuel indication system
serviced.
Turn your ignition to OFF while fueling to obtain an accurate
fuel gauge indication. If you do not turn your ignition off, the
fuel gauge will not display the new fuel level immediately, but
will slowly increase to the correct value.
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