My friend was building a new system. And like many new builds when you haven’t done one in a while, not everything went as smoothly as it could have. Here’s how he solved a phantom CPU fan error.

CPU fan error? But the fan’s working!

CPU fan error

On this motherboard, it’s pretty clear which header is for the case fan and which one is for the CPU fan. Some boards put them closer together and don’t label them as clearly. But Dell motherboards may give you CPU fan errors if you try to use a non-Dell fan on them. I’ve tried it.

A couple of things can cause a CPU fan error even if the fan is working just fine. CPU fans have several connectors, with different numbers of pins in them. You can plug a connector with fewer pins in and get it to work. But those extra pins help the system to sense if the fan is working and to throttle the speed. Some motherboards are picky about those pins being there. Now, if you bought your components together they’ll probably work together OK. If you cobble together something like my famous Dellpaq, you’re more likely to run into this. I certainly did.

My friend wasn’t Frankensteining a system together. He bought a bunch of new parts that were all designed to work together. What we found was that the case fan and CPU fan headers were pretty close together. And while the two headers were marked, they weren’t marked in huge print. We aren’t in our 20s anymore, so he plugged into the fan header that looked right at first glance. It turned out the right one was the other one.

The fan headers are interchangeable, so you can plug into the wrong one and it will still work, but the system is far more likely to monitor the CPU fan than the case fan, so you don’t burn up a CPU. Your system can last a lot longer without a case fan than it will without a CPU fan. When I mentioned he may have used the fan header, he looked again closely and it turned out that’s exactly what he did. He moved the fan to the CPU fan header and the error went away.