the trobled unit is dell e520. After I read the bios error message I noticed there was a cpu temp err back in may but only once. when I 1st read this message, the fan can still ran at maximum speed(very loud). I assume its broken( guessign the temparature senser inside is bad) so I took it out , undust cpy heat sink and fan area. Replace with brand new unit(made by delta de1212xxx). turn on, still show up message. So I cleared log and boot to window. the new fan still run very loud. So I start virus scan and uninstall application. after 40m, during mid of uninstall.. it become quiet again. I thought it is solved.... but the fan back to loud th enext day and never came quiet again. I checked cpu speed, its at 31C( the fan is blowing very hard at it). I tried cpu fan monitor program but it cant find the fan. Only report the temparature is ok. I checked web and many similar question had been asked over the years. The problem is the case is not solved even with new fan replaced.
You may have a fan speed adjustment in the motherboard bios. Press the "del" key or whatever key is listed at the top of the post for a couple of seconds while posting. Look for a hardware monitor section. Enable any fan speed setting, then set all the possible listings to a low number. I use 4 as a maximum setting, and 0 or 1 on others. I don't mind higher temps, as my case has other fans that can move air. The fan speed control only works on fans connected to the motherboard with a 4 pin connector. Amd boards don't have this feature. For them, I use a zalman fan mate rpm adjuster.