I think there was no Flexible Service System on the '97 C-Class -- that it wasn't in those cars until '98 (at least in the US -- are you in Europe?). There certainly wasn't any in my C230 with the normally-aspirated engine, and no mention of it in the owner's manual or in the dealer's literature. I changed my oil 3-4 times a year for 3 years without having to reset anything.

Unless MB put that system in some C-Classes as an option, I doubt yours has it! You can change the oil without worrying about that.

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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