The FOMC consists of 12 members.
- The Board of Governors. 7 seats are allocated for it, however currently only five are taken. Members should be appointed so that a "fair representation" of "financial, agricultural, industrial, and commercial interests, and geographical divisions" is given and have to be accepted by the senate. (http://www.law.cornell.edu/uscode/pdf/uscode12/lii_usc_TI_12_CH_3_SC_II_SE_241.pdf)
- The Reverse Bank Presidents. 5 seats are allocated for those, with a yearly rotation on 4 seats, ...
I was unable to find out how exactly this committee votes. It's official documents state that it's internal organization is determined by itself (http://www.federalreserve.gov/pubs/frseries/frseri2.htm) - I would guess that this also includes how voting about individual actions is performed.
For a new policy to take effect a consensus has to be reached. Policies are voted upon independently as shown here: http://fraser.stlouisfed.org/docs/historical/nara/bog_minutes/19511227.pdf or http://www.federalreserve.gov/newsevents/press/monetary/20080130a.htm
It doesn't need to be unanimously - http://www.federalreserve.gov/monetarypolicy/files/FOMC20080121confcall.pdf shows dissent from President Poole/St. Louis Fed.
Is there a implicit meaning of consent - e.g. 50% or two-thirds?
Is it in accordance with the law to not fill the two spots of the Board of Governors? If those aren't taken then the Reverse Bank Presidents effectively gained power.