On my '86 420SEL, the light would come on with 4 gal. left in the tank, despite the manual's statement, if I recall correclty, that it would go on with 3 gal. left.

I love a car that warns you early.

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-- Paul W. (The Benzadmiral)
('03 Buick Park Avenue, charcoal/cream)
Formerly:
'97 C230, smoke silver/parchment; '86 420SEL, anthracite/light grey; '84 280CE (W123), dark blue/palomino