Bill,

That happens in my 1982 240D when I have a bad glow plug. An independent mechanic once told me that was built in to the relay to let you know something was amiss. If you have to do it more than once you have more than one plug out. I typically replace them all when I get the signal, just because it always happens when it is freezing out, and the car really doesn't like starting with glow plugs not functioning. And my daughter has it in Upstate NY now, so the cost of a few extra plugs is nothing compared to a frantic daughter looking to have a local shop do the job. 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)