marea 1.6 automatic '160000 k"m.

problem:
when trying to go up to 4th gear level - it couldnt .
the red transmission warning light is blinking ,than when stopping the car moves heavily.
when starting the engine and limiting the gear lever to 3 the car runs smoothly and no red light blinking .(good for city driving )
the trans' liquid is clean& pink (not black)
question:
is it inside the transmission or "lighter" problem
thanks
moni