This forklift just stopped moving, no fwd, no reverse, just the backup alarm. Still have hydraulics and steering.

The only fault code showing is a -04 with a green light on the little wrench on the display.

Before I start just blindly tearing into stuff, can anyone tell me:
1. What this code means
2. Why it's not listed in any manuals, books, or forums I've searched so far?

In one book with a fault list it jumps from -03 to -05. Almost suspicious, you might say.

Thanks in advance