Engine will not even turn, radiator fan runs, just replaced battery.

when you removed battery,did you remove key from switch?also did you unhook neg. first and pos. last.and did you install an AGM TYPE BATTERY?hooking back up,pos.first,and neg. last.some of the mercedes also require hooking up a battery saver,before you unhook the battery to keep presets.these cars are very very sensitive,very.

It's most likely the K40 relay. I had the same issues with my 02 SLK 320. Just fixed it today by pulling out the K40 relay and giving it a good going it over. I checked all the fuses, then I opened it up and looked for burned solder connections (there are how to instructions on line). I didn't find any problems so I cleaned all the connectors and the contacts for the fuses (electronics cleaning spray) then I re-installed everything, and made sure all the connections were tight. The car started right up perfectly on the first try.

I experienced the same problems recently. Had to replace the crankshaft sensor again because the new one was faulty. Car began working properly for about a month then started happening again, had to replace the Camshaft sensor also. Have had no problems until battery got low. bought a new battery and car would not start. Called Mercedes tech and was told to jump start the car, even though it had a brand new battery. Worked like a charm!