Mercedes-Benz 2005 M-Class Operator's Manual page 222

Operation
At the gas station
Replace the fuel cap by turning it to the
right.
You will hear when the fuel cap is tight-
ened.
Close the fuel filler flap.
i
Only use premium unleaded gasoline
with a minimum Posted Octane Rating
of 91 (average of 96 RON/86 MON).
Information on gasoline quality can
normally be found on the fuel pump.
For more information on gasoline, see
the Factory Approved Service Products
pamphlet.
220
i
Leaving the engine running and the fuel
cap open can cause the yellow fuel
tank reserve warning lamp to flash and
the ? malfunction indicator lamp
(USA only) or the ± malfunction in-
dicator lamp (Canada only) to illumi-
nate.
For more information, see "Practical
hints" ( page 254).