For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Could be anything on the same bus.
Even PCH can have internal problem, or bad connections on that bus.
Change all is possible.
If still the same, explain to the client how to use the fan control software...