I had a HP laptop that was giving a system fan failure message on boot. The service code from HP was 90B, but related codes on HP’s website show it might also be a 900, 909, 90A, and 90F code. The CPU fan would spin up and down constantly and the CPU speed was capped at a very low speed. This made the laptop very slow.

I fixed this by disconnecting the fan and hard drive, turning on the notebook computer, then turning it off, and re-connecting the fan and hard drive. After doing that, everything worked just fine. This simple fix might work for other laptop computers.

There are some others things I recommend doing while you are doing all this.

First, while you have the cover off, make sure you blow all dust out of the internals of the computer. And tighten the screws around the CPU fan. If the computer is over 5 years old, you probably should remove the CPU heatsink and put fresh thermal paste on.

Second, go ahead and clear the CMOS while you are there. Remove the CMOS battery, if one exists.

Third, just for good measure, update the BIOS or UEFI. It is also possible that a BIOS flaw can cause the system to not properly monitor fan speeds and temperatures.