My crankshaft position sensor has gone out, how do I locate it? I cant find it!

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My truck stalls then starts after about 20 minutes. It started on the highway 1 hour 30 minutes from home. I waited 20 minutes and drove about 20 minutes until I got home. It sucked! I need assistance locating the sensor on my 2001 Mercedes ML55 AMG. Every link says its simple, and on youtube they don't show my truck. My truck has a very tight fit along the firewall and has the radiator reservoir on top along with brake lines and fuel lines in the way. The mass air flow is behind the engine under the reservoir. My problem is locating the Crankshaft sensor somewhere in that mess. Do I go from underneath in this engine? I see no way of getting to it or even locating it from top.