2005 e500 won’t crank over
 

My e500 w211 has recently developed a problem on colder mornings.
Car won’t turn over. And i get abs and esp warnings. Also all the leds for the airmatic on the console are on

I’ve noticed if I leave the key on the cooling fan will eventually start up and run for a while ( car is at 50 degrees f! )
After a moment the fan stops and the car starts just fine .
Most recent change was replaced battery a few months ago ( not oem) but I had a similar issue a few years ago that mysterious went away..
Having a similar problem with a us car that did this when overheated , I’m Wondering if there is a bad sensor making the car think the engine is overtemp. ?
Any suggestions much appreciated
Bob

if the cooling fan is switching on at full blast - and you have errors on the dash, you probably have a situation where the engine ECU is going offline.

In my experience it can be either the ECU itself or moisture or water in the fuse block in the door jamb which is intermittently cutting out power to the ECU when cold.

Ive seen both, but the above is not exhaustive. to identify the issue you will need to see if the ECU is actually providing reference voltage to various sensors.

I swapped the starter relay and it started.
I then tried to start it without the relay in. After a few seconds the cooling fan started.
Put swapped relay in it started.
I’ll change relay as a starting point