It could be either an Imaging Unit issue, or developer issue.
First, I would recommend swapping your yellow Imaging Unit with another color (they are all interchangeable) and run some test prints, if the issue follows the Imaging Unit, you'll know it's bad and needs to be replaced.
However if the issue stays in the yellow color position, it may need to have a service visit. In this case, give our support line a call and they can take it from there.
Hope that helps!
It could even be that the yellow IU contacts were dirty and just by swapping them around it cleaned the contacts off and is now getting a good strong charge. Let's hope that's the case! :)
My Xerox 7300N was having a yellow streaking or smearing issue. The yellow portion of a color image was off-register and had a bit of an "out-of-focus" trailing smear. The smears ran in the same direction as the paper transport direction. The off-register distance was small at the top of the page (only about 1/8") and was progressly greater as you moved toward the bottom of the page (an off-register distance of as much as 1').
I reset NVRAM and that fixed it!