Is this a gasoline only truck?
Do you have a digital hourmeter or is it a mechanical one?
I am guessing the code is the O2 sensor being out of range due to the fuel mixture being too rich/lean and we need to go back to the fuel system and look at contamination/fuel quality issues. replace filter, drain tank completely and discard gasoline, flush all contaminants, look at where they are getting their gas from and how they are fueling their machine. If they are filling it with jerry cans from some cheap-gas independent corner station, suggest Esso/Shell and more careful refueling methods. Check your email address as well, my email to you bounced back undeliverable.