Mercedes-Benz 2003 C 240 4MATIC Operator's Manual page 302

Practical hints
Flat tire
Wheel cover on vehicles with steel rims
(Canada only)
Position small wheel cover opening
over tire valve and press wheel cover
against wheel rim.
Now press (do not hit) opposite side of
wheel cover against wheel rim until
seated.
Make certain that the springs of the
wheel cover are firmly seated in the
outer rim of the steel wheel.
302