Mercedes-Benz 2001 ML 55 AMG - Manual (Page 223)

220 Malfunction and indicator lamps
Technical
data
Instruments
and controls
Operation Driving
Instrument
cluster display
Practical hints Car care Index
Fuel reserve warning When the warning lamp (1) comes on after starting the
engine, or if it comes on while driving, it indicates that
the fuel level is down to the reserve quantity of
approximately 3.2 gal (12 liters).
See page 212 for notes on refueling the vehicle.