I'm not so sure it is a sensor issue, no. Were you able to get the newest version of firmware loaded on your machine using the link that I posted the other day? If so, how did the update work?
Do you remember what firmware version was on your machine before all of the trouble started which led you to trying the upgrade in the first place?
Also, if you are able to - can you please print a Start Up page for me and let me know what the total page count is on your machine?
Your light prints may be due to that toner cartridge. Was it a brand new unopened/unused cartridge when you put it in the machine the other day?
danny, I forgot to mention that the toner cartridge that is in your machine right now will continue to display the message that it is low even if it isn't - following the upgrade of your firmware. I think BenjaminG already mentioned that, but I wanted to say it again. After you complete the upgrade to firmware PS 4.11.2, you will need to install a new toner cartridge.
I hope that this resolves your issue. Please post back and let us know how it works out.
If possible, you need to load the newest firmware on your machine. Click the link below; that will take you to the Drivers and Downloads page here on Xerox.com/support. On that page you can download the PS 4.11.2 firmware version. This version has the fix for the "Premature Toner Low Message" that you're seeing.
Click here to download the firmware.