I have one "good" key for my 1998 E300D Turbodiesel, and one that went through the wash and is now a "bad" key. The "bad" key will still run the car, it just won't work the doors. But it came with a little switchblade old technology key to get in the door, so I can use the door locks like an older W124 and earlier MB, while the gizmo in the blunt end that goes in the starter spot stll works. I understood there is some inert thing the car's starting key hole reads and responds to. Not sure if it has any electrical functions, as my "bad" key is really dead, electrically and it still works starting the car. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)