it starts the transmission in a higher gear to prevent wheel spin.. only works when you are in D... while stopped in D press it, light will turn on.. your rpms will rise very slowly and you wont get much acceleration (like if youve driven a manual and forgotten to put it back into first after a quick stop) then once you hit 20-25 mph it will turn itself off and your transmission will act normal again.... it will not turn itself back on automatically