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.
This happened to me with 01521 board.
I finally found a shorted signal from a speaker amp to T2; it was located inside T2.
Was impossible to complete DFU on it...
I had one with T2 shorted on SPKRAMP_RESET_L; caused by leakage from PPBUS_G3H in audio board.
That one I got it working after complete DFU,
Of course, no speaker sound, only headphones.
The one above mentioned (previous post), never complete DFU and was impossible to repair it.
T2 found shorted on a line corresponding to the other (onboard) speaker amp.
However, on other service, both boards have been connected in the same shell, with liquid damaged audio board and flex.