My mariner has shifted a tad bit hard since i changed the transmission fluid a few months ago. the other day it went from not to bad to wont shift into second without letting off the gas petal. when i do that it shifts smoothly and the rest of the gears work automatically and smoothly. i did notice it had very little fluid so i topped it off but the problem still persists. and the wrench light is on but my scanner wont pull any codes.