My understanding is that the ECB’s Governing Council operates by consensus, although a procedure is in place for a majority vote to determine the course of monetary policy.
So far, the ECB has maintained the principle of one member, one vote, with the six Executive Board members and the twelve national central bank presidents voting equally regardless of the economic size of the country that they represent. The ECB has had to wrestle with how to adjust voting as the euro area expands over the next decade or so.