hi i have just bought a 300zx twin t h reg and my auto box is playing up the car drives fine but it does not want to go into 3rd and 4th gaer in my auto box but first and second are fine it stays in second and does not even change to 3rd or 4th shall i do a auto box diagnostic check or what please guys help me

may want to put this in the advice section mate, would help if i could but know nothing about autos