Komatsu WA500-3 low fuel pressure

I'm doing this for my husband who is at working trying to fix this Komatsu WA500-3 wheel loader right now. He said that it is giving a low fuel pressure rail code. How do you fix it? Or does anyone have the computer schematics that I can send to him or you does not matter. He works for a mining company and they have had four guys already look at it with no luck as to why or how to fix it. My husband is usually an operator and not a mechanic but no one seems to know how to go about this. We need help!!! Please. :)

Thank you

A very loving and supportive wife

Serial number is 52133 if that helps I do not know the year. He is trying to figure that out as I type.