I have a 2000 ML55 that has had a multitude of problems (see my previous post ML55 Nightmare). After having $9K worth of work for a stalling problem, the car died again. It would crank but not start. After waiting 5 min. or so, it would start and run fine. MB has the car back and thankfully it happened while they were looking at it. They believe that the key is defective. Apparently, the key sends a signal to the ECU that allows it to start. MB is telling me that since the key is bad, the car is in effect going into "anti-theft" mode and will not start. I asked if the bad key could stall the car while it is running and they say yes. This doesnt seem logical to me. I could see if it was one of the electronic keys on the newer MB's, but I thought that since my key has a pop-out metal key, all the transmitter did was unlock the doors.

Has anyone ever heard of this? Is MB right? This problem has been making me nuts. Thanks

i would say they are wrong, i have seen too many newer mercedes V-6 and V-8 engines with the same exact problem, the fix every time was the crank postition sensor. if it were in anti theft mode the engine would start, run a few seconds then die. also to see if the key is authorized, when you turn the key on, the little red light at center dash blinks once, this means start is authorized. also they can look at the actual values for the aam and see if drive authorization is enabled.

Check the coolant sensor. I'll bet you it is bad. It is located under the air pump front of the engine. This will cause that problem, you would set codes if you had a communication problem.
GVB

There were no codes, but they did tell me that the dash light indicating key recognition was not on. Crankshaft pos. sensor is new...

So you have had a communication light comming on? Well there you go. Change the batteries reprogram and see if it works. If it doesn't you may have a bad comm module/buss. You need to kinda tell people what lights/codes are coming on if you want an acurate answer. This has nothin to do with a crank sensor

If your problem occurs primarily when the engine is cold the ME control unit may need to undergo a program flash (remapped parameters) or possibly exchanged. You may want to have your local dealer investigate any bulletins which may apply to your current problem.