Configuring the FAULT pin as an input pin via the MFR_FAULT_RESPONSE(register 0xD9) Bit0 = '1' will force the fan output to 100% duty cycle when the pin is externally asserted. Bit 0 of the MFR_FAULT_RESPONSE register must be set to a value of 1 for every page (channel) that the 100% duty cycle behavior is desired when the /FAULT pin is drive low. Since FAULT is an active-low, open drain input/output, the way to force the 100% duty cycle would be to tie FAULT to VDD via R_pullup and then pull it to ground to assert.