I doubt you'll find the actual circuit diagram for the module, LR don't show it.
You'll be working blind to fix it, but if you break the circuit into sections, and test the components in each section, you might get lucky.
Presumably you've checked all the fuses in the vehicle before condemning the fan module? They aren't know for unreliability as a rule. In my experience, the fans themselves are more unreliable than the electronics driving them.