The crankshaft position sensor may fail. Symptoms of this are: The engine will crank—but not start—especially when the engine is warm. The car may start again if it is left to cool off, but it may run roughly or have poor performance. Communicating these specific symptoms to your technician can save diagnostic time.Google+
Car Problem Reports
Mercedes-Benz C240 4MATIC Engine Performance Problems Due to Crankshaft Position Sensor Failure
Mercedes-Benz C240 4MATIC Problem
Average Mileage: 72,637 mi (58,744 mi - 83,267 mi)
Visitor, 2005 Mercedes-Benz C240 4MATIC, 58,744 mi
Crank sensor failed, $55 dollar part stranded car on the hottest day of the summer. Towed and repaired same day.
Visitor, 2003 Mercedes-Benz C240 4MATIC, 83,267 mi
A similar scenario occurred with my C240. It stalled while at a red light in the middle of rush hour traffic with my 1year old in the backseat. After having it pushed out of the street, the car started again about a hour later when roadside assistance arrived. The car drove for 10 to 15 minutes then stalled again. The MB service advisor said it was the crankshaft or the crank shaft position sensor (I don't remember which). Repairs were covered under The extended warranty minus the deductible of $75. Car seems to be working great. It's only been a day so I'm hoping this was the fix it needed. Still love my car, but ready for something newer and hopefully more reliable.
Visitor, 2003 Mercedes-Benz C240 4MATIC, 75,900 mi
No other problems with the car since I bought it in May 2003, until this occurred in July 2011. After sitting in the sun for an hour (on a hot 95 degree Michigan summer day) car cranked but did not start. Called roadside assistance, they arrived 15 minutes later and the car started with no problems; no jump needed as the battery was working fine. A few days later, same thing happened in similar weather/timing conditions. Called roadside assistance but car started before they arrived, however the "check engine" light came on and stayed lit. On days in between, the car had been starting/running fine (usually car had been sitting in a cool parking structure or garage). MB Service diagnosed it as a crankshaft position sensor failure. Replaced sensor. Entire job took about 1.5 hours and cost $350. We'll see if this eliminates the problem.