Xerox 5028 error code U9

[Mr Spock]

U9-3
Xerographic process problem.

The Exposure sensor detected low Exposure Lamp intensity. Switch the Main Power Switch off then on in order to clear the Status Code. Go to the U9-3 Xerographic Process Problem RAP

U9-4
Xerographic process problem.

The Main PWB sensed that the Toner Dispense Motor was not running. Perform 20-3 U Codes Clearance . Go to the U9-4 Xerographic Process Problem RAP

U9-5
Xerographic process problem.

The CSDC zero point was too high during auto setup. Perform 20-3 U Codes Clearance . Go to the U9-4 Xerographic Process Problem RAP U9-5 Xerographic Process Problem RAP .

Hi there
Does anyone know what the error code for U9 means and how to clear it?

Thanks alot
Susan