I know this is an old one, but i want still write this, if theres any help to someone.
First you take your multimeter, and check if pots are working. If they work, there is the green parts in the pot. There is a crack/slot in the green part, just open it slightly, so the pot wont move with axel. Make sure it moves zero with axel, so the shifter will work perfect. Its really easy to fix. There could be some fault on the wires too, check them out.
