Alright, I know this is the Diesel Forum, but a friend did a transmission job on his 1992 500 SEL. Now it won't start. Checked the Crank Sensor and it's okay. Battery is fine. What could be wrong?

I am really not too familiar with automatics, but I believe there is a switch or sensor to detect that you are in Park or Neutral that must be engaged to allow the starter to crank. Try putting it in Neutral and seeing if that helps.

By the way, will it crank or not? I mean, will the engine turn over with the starter and it won't fire, or will the starter not respond at all? 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)

The starter engages, and motor turns over, but will not start. Could it be an electronic problem?

Got Spark?

Also check the O2 sensor cable or cable that carries the line to the O2 sensor
I saw a case where a wire got pinched and that prevented the car from running, on a 560SEL.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!