What is the e.c.o. button by automatic shift for? and when pushed lights up on tash board
It is most likely either an economy mode for long-distance driving, or an electronic stability/traction control mode. Call your Subaru dealer to ask them, they will be able to tell you at no cost.
Search Subaru Outback Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Subaru Outback Experts