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.