The Y470 brightness adjustment is not working properly. It was working fine out of the box. The on-screen-display is stuck at 3 and not going up or down despite changing the brightness.
Ensure that you only use the official Lenovo drivers. However there is a possibility that a Windows Update was done by Microsoft and the Intel drivers has been updated to their version instead.
Do try to do a driver rollback on the video driver to fix this issue.
If problem persist after doing a rollback on the video driver, do uninstall previous version of video driver and Lenovo Energy Management reboot and install the Intel Video driver from Lenovo support site and the Lenovo Energy Management driver.