See this thread, someone with a similar problem to you:
http://www.fixyourownprinter.com/forums/laser/24105
I'll summarize the solution:
The "software" H4 problem is quite common that Xerox has a resolution on its website
Solution: Perform a Fault Reset 14
Performing a Fault Reset 14 will reset your WorkCentre and will help to clear error codes.
1. Find the pink Clear button on the Control Panel of the WorkCentre.
2. Find the button below the word Auto.
3. Press these buttons in the following sequence: [Clear], [Auto], [Clear], [Auto]
NOTE: All of the lights on the Control Panel should go out and the LED Display should go blank. If the lights do not go out, then repeat step 3 until they do. It may be necessary to increase or decrease the pace of the [Clear], [Auto], [Clear], [Auto] sequence.
4. Press the [10's] key one time and the [1's] key four times to enter '14' in the LED Display, as if you were to make 14 copies.
5. Press the green [Start] button.
6. Press the pink [Clear] button two times.
7. The WorkCentre should now warm up and come to ready.
8. If the above steps do not clear the error code, repeat steps 3 to 6 a second time.
