Hi everyone. I'm hoping to get some advice.

Car is a 1999 e320 2wd. About 190k miles. I owned it for two years and put on about 20k. A few months ago I sold it to a family member. She put on a 1000 miles. Parked it one day. Now it will not crank over. Key turns in ignition just fine. The cooling fan seems to run on high. I read that maybe caused by ecm not being powered? I cant seem to find alot of info on this problem, besides k40s, battery, and key fobs.

Things done/ checked: Battery fully charged, also switched out with a new one, Tried a used junkyard k40 relay from wrecked car, jumped small square relay on k40 unit to engage starter. (engine cranks over fine), removed the range switch inside of the shifter and cleaned, every fuse I can find is good, There is no spare key fob.

Nothing has allowed the engine to crank. Hoping someone can point me in a direction to find out problem. I'm a bit lost.

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Dave

1985 190D 2.2 auto--gone
1975 240D 4-speed--storage
1985 500SEL--daily driver
1985 300TD--bad rust, soon to part out...
1982 300SD--waiting on engine from RD
1984 190E--storage
1996 Dodge 2500 Cummins--daily driver

If you jumped the starter relay and it then cranks, shouldn't you replace that relay?

I think you have verified every reasonable culprit: key, k40 relay, starter relay, starter wiring and grounds. If none of those are it, it could indeed be the ecu, and your best bet there is to get it scanned.

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Prost!