dear friends, I solved the problem. was actually obstruction by air.
the printer has a resource for the problem, under Maintenance, under System Cleanup.
is the ultimate maintenance feature, and the one who spends the most ink, on average, 25% of the ink reservoir per use. in this case, those of color.
but I warn. the resourse does not work in 100% of cases. the safest solution is a manual intervention, shown in this video (in Portuguese). https://www.youtube.com/watch?v=6TTxgDKY8Tc
I'm partially happy because I do not have to take an authorized service.
but partially disappointed to face this problem on a printer with 15 months of use, and regular use only.