Error: CPU fan has failed! PC will automatically power down

Question

All of a sudden my HP Pavilion a6357c has started having issues with the fan. Whenever it boots up, the error message in the title appears and the computer powers down. After a few attempts the computer eventually turns on and runs fine, but clearly a problem exists.

I've looked around, but all solutions end at the user changing the BIOS settings to a lower fan level, a feature which my BIOS does not support. I run Windows 7 Home Edition on an otherwise unaltered machine. Is my power supply too weak, or maybe the connection in some wire growing old? Help diagnosing would be appreciated.

Edit: Fan is not broken to the best of my knowledge. It always spins up, though it's speed varies which I think is normal. I heard this could happen if there is inadequate power. How would I diagnose that? Oh and it's as clean as I can get it :)

Solution

Some fans have a built in speed sensor (tach) that feeds back a signal to the Motherboard. This lets the Motherboard know that the fan is actually rotating and at what speed.

This is typically done by having a tiny magnet attached at the hub of the fan blade. As the fan rotates, the magnet comes near a magnetic sensor (hall effect) on the motor housing or mount. This is also done with optical components rather than magnetic.

As a fan is used, a typical wear point is the bushing (or bearing) where the motor shaft extends out from the motor to attach to the fan blade hub. This wear can let the fan blade move closer to, or farther from the motor housing than it was designed to do. As a result the speed sensor can fail. Starting and restarting the fan (computer) could eventually let the fan blade move into the proper position and it will begin working. So, the fan could appear to be working fine (mechanically) but actually have a problem.

Fans are pretty cheap compared to other repair components so, depending on the age of the computer, I would just try a new fan and see if it was the problem. If you want to be sure, I would take the computer to a small PC shop and buy the fan and install it on the spot. You should know pretty quickly if it was the problem.

I don't know if you have working relationship with PC shop. The one I use would be happy to take a test fan from their workbench to try it out before I needed to buy one.

Your particular fan may or may not have a speed sensor but I suspect that it does. Systems that do not monitor fan speed will usually monitor CPU temperature instead. As the CPU temperature increases, the system drives the fan faster and faster. If the fan isn't spinning fast enough (or not at all) to properly cool the CPU, the CPU temperature will eventually get too hot and the system will slow the CPU way down, or display an error message and halt the computer. But, it is not likely that the CPU could heat up quickly enough for the failure to show up at boot time.

Comments

[ganesh]

Did you check if the fan actually has failed? If it is broken then the obvious solution would be to replace it. If it is not broken then you really want to add that to the original post.

[ExitFailure]

That makes sense, I will try it!

[ExitFailure]

What kind of fan would I need? I can't find any information about the type of fan anywhere on my computer :(

[Kevin Fegan]

It would probably be cheaper if you could remove and reinstall the fan yourself. Bring the fan to Fry's or Best Buy. Also bring the computer with (but leave it in your car) in case they need to see it. But my first choice would be to take it to a small PC shop. I find they give the best and most helpful service and they don't always charge you for every little thing they do. Wherever you go, make sure to check their price first and shop around if you feel you need to.

[Kevin Fegan]

@ExitFailure how did this work out for you ... were you able to get your fan working or replaced ?

[ExitFailure]

I got the fan replaced, but it fixed nothing. Turns out there were 2 fans, so maybe the other one was the problem. I kind of gave up for the time being...

[Kevin Fegan]

The error message and failure to bootup implies it is the CPU fan. Are there 2 fans on your CPU ? Which fan did you replace ?