Just an update on my fan issue which I shared about a week ago...
Mechanic did the temperature tests and electrical testing to conclude that all fan and cooling system parts were fine, just as I told him from all of my multimeter circuit checks and temperature checks. No fan action whatsoever, even with A/C button on.
He then went ahead to test the A/C pressure. Found the pressure to be low - approx. 0.9 lbs when it should be 1.3 lbs. He topped up the pressure and retested. The A/C started blowing cold air (obviously), but more importantly the fan started working normally again! Yesss!!!
I am super relieved and happy that she's good to go on longer trips now as I had to stick to really short drives for quite some time. I commented that it is really stupid that a cooling fan stops working because the A/C pressure drops a little (below a threshold) without tripping a code. It's a really dangerous thing as it can go slowly and unnoticed causing repeated overheating and damage to many parts (note: I am now getting new exhaust manifold catalytic pipes and post-catalytic oxygen/lambda sensors put in because they were all toast -- expensive job). He said this is how it should be set up. Not sure if I will ever understand or agree with that.
Anyways, I hope this helps someone who is having fan function issues in an e90 and has checked every component and remains scratching their head. Do not neglect the A/C system... check the pressure and make sure it is where it should be.