When my 2017 mazda6 was returned to me the HUD was blank( nothing was visible on it). The display lens did not close completely and it was tilted back (towards the windshield) too much. The dealership, which is 45 miles from me, says that it can cost up to $2,000 to fix. Of course the valet company says that once you leave the property they are not responsible. Soooooo, I held the lens down for a couple of seconds while starting the car and voila- it's fixed. Of course, I cannot and do not recommend that anyone else try this.
