Had key malfunctioning problem on my 99E320 at 40K miles.
When key is in ignition and turned, cannot fire up the engine. The starter keeps cranking without you holding the key. The battery and starter are good.
My friend experienced similar problem with his ML and said there is a malfunctioning chip inside the key and not recognized by the engine resulting in sending an engine kill signal to disable the car, an anti theft design. He ordered new key from the dealer with programing at total $120.
Drove to wife office to get 2nd key and it worked and fired up the engine. After that, the first key also worked.
A week later, it happened again. Now both keys don't work. So it appears not to be key problem.

Stranded at night, called MBZ 24 hours service. Operator instructed to use manual key to lock and unlock the door, then use the original key to start again. Won't work and MBZ operator now says it is the fuel injector/engine not getting gasoline and the car must be towed to MBZ dealership for repair.
As there is no dealership service open at Saturday night, return to car after dinner, 3 hours later. Using original key, the car started, and the second key also worked.

What seems to be the problem? The keys, or the engine will start only when cold or 2-3 hours after the engine cools down?

Someone also suggested in case of car computer problem showing malfunctioning display, disconnect the battery and reconnect after 5-10 minutes. The computer will reset itself. Would that solve some of the problem?

It happened again and this time the starter keeps cranking and died after 10 sec.

Called MBZ dealership and the service writer advised it could be the crank sensor or fuel injector and the car must be brought in for diagnose. What seems to be the problem as the car will start after several hours.

 

the best step now is to take it to dealer and read the fault code memory.

by then we can narrow down the suspected malfunction.

it can be fuel system, drive authorization system or on ignition side.

your car is 210 model...right?

try synchronizing the key also.

 

Thank you for reply
Yes chassis 210 US Model
If car can start after couple of hours, it should not be fuel system, right?
What is drive auth system?
and how do I synchronize the keys?
How does a Crankshaft Sensor look like?
Your insightful advice is much appreciated before I take the car to dealer.
Best regards.

 

drive authorization system is the anti-theft.

it dis-able the fuel injection if the random key code doesn't match (key and control unit). the reason why i also say fuel system

i have posted the procedure here before. try using the search function.

the crankshaft position sensor is on the bell housing of the engine, near the transmission. it is a small thumb size pick-up unit.

good luck with the diagnosis.