how can i fix the automatic gearbox of renualt scenic?

You probably have a DPO trans. The band has broken. To verify, hold the selector lever just out of drive. This should provoke 3rd gear after a couple of seconds. Still holding the lever between positions drive to 30 mph then release into 'D' and you should be able to go onto 4th. If its a bit tricky to hold lever against its natural position, just unplug the computer (purple sliding retainer). Ensure not in park as shift lever locks with no power.

mags
January 2010