Yes, it needs a tachometer. Make sure you get the pins correct or you could damage the fan circuitry. The wire colors should be red=+12V, black=Return, white=tachometer. And on the chassis circuit board, the connector pins closest to the large capacitor (pin 1) is +12V, the middle pin (2) is return and pin 3 is tachometer. This is for if you have a PXI-1042, NOT a PXI-1042Q, so look for that.
I have the same problem but with a PXI-1042Q Chassis. In my case, the three fans are working. What do you suggest me?
Thanks for posting your question on the PXI discussion forums.
However, I would suggest for you to start a discussion on a new forum. This discussion is slightly older and therefore does not get as much visibility in our community. If it's a similiar problem I would recommend referencing the troubleshooting steps suggested in this forum on your new post.