In my opinion, its designed to run fan when the battery is charging or the battery charge heats up the laptop and fans are supposed to run when heat is generated inside.

Thanks for reading.

alekum:

You are probably correct in that the temperature info from the GPU is disconnected when video is switched to the on-board video, and the fan circuity doesn't get the expected signal till you turn the Nvidia GPU back on. You might want to try updating the video drivers for both. If the Dell Nvidia driver doesn't work, you could try getting the latest from Nvidia itself. Usually, Nvidia drivers will work fine, but sometimes Dell has the drivers modified for some special feature, and you would have to revert to the Dell version.

Are you still under warranty? What OS are you using?

Did you update the chip-set driver?

I had the same problem with my Dell 5558. It had a wild and unpredictable fan response, sometimes it activated too late sometimes it didn't slowed down after load was over and kept running at full speed. BIOS updates A07 didn't fixed it.

My solution was to use SpeedFan, in settings options there is a checkbox for "dell support". By using SpeedFan you'll find out that the fan only has two speeds, slow 2200 rpm and fast 4800rpm, no in between. I configured it to set the fan at full speed after a temperature of 45 degrees at the CPU, my idle temp being around 35 degrees. Also notice that I keep my fan at at least 50% half speed 2200 rpm all the time, because there is a 0 rpm setting too.

This setup is much butter then the original fan controller which either activated too late or as you complained forgot to slow down. For example now my max full load temps are around 58-60 degrees instead of the original 70degrees, because the fan activates faster.  Also now it properly slows down after the load is over. One of the reasons I love Dell laptops, full control over the fan speed.

Ofc I will have to change the 45 degrees temp in time as my idle temp goes up, but for now it suits my needs.

The fact that a fan control program helps indicates the the problem may very well be in the BIOS, as the fan control program resides in the BIOS. I should have suggested this earlier, as I have solved fan control issues several times in laptops using these utilities. However, I didn't dwell on this solution as many Dells can not be controlled by these programs because of non-standard designs.