One of my fans on my macbook does not work.

I often notice that while one of the fans on my macbook is going full blast, the other one is silent. This seemed wrong, so I downloaded macs fan control to see if I could manually control it. However only one fan shows up on the menu. I've looked in the apps settings to try to add new fans to the menu, but it can only detect the one fan.

If anyone knows how to fix this problem, please let me know.