I'm just going to hijack this thread if you don't mind...
I've also got a 5FB15 in the workshop that was throwing error C0.
We replaced the CPU board, started getting C0, E0, A9.
Also tried replacing the DC-CD board, SDD board and even the main transistors.
Nothing changed.
Also cleaned contactor tips, still nothing.
Power diodes seem fine, as do the capacitors and resistors. Tried connecting a new battery, no effect.
Even ordered another CPU board replacement thinking the first came faulty.
Funny thing is when I was measuring the CN109 on the SDD board, I shorted two pins (oops!) and then the error was gone - for a few minutes. The forklift operated normally in that time.
At this point I'm completely out of ideas.