renault sonic auto?

check for any oil leaks around g/box, and check oil level. if leaks found then you will need to fix them and fill g/box with correct type/amount of auto transmisson fluid, when you have done this, you need to start the car, and keeping the brakes ON, move the gear lever though the gears to allow fluid to settle thoughout the g/box. if this does not cure the problem, then you need the services of an auto trans techie, which ain't cheap.

hope it helps
October 2010