Reverse gear (auto box)

before getting involved with gear box check rear brakes for sticking jack up car revolve rear wheels in both direction to make sure they are free as it is not unknown for the lineing to come loose or come of the hand brake shoes if ok check the fluid level in the gearbox and check if it smells burnt it might be a good idea to have the gear box oil changed it uses a special fluid i think it is texaco N402 or transmax j you must use the correct fluid as you can not drain it all due to the fluid in tourqe convertor change run for say 200 miles and change again you could go down the diagnostic route as there could be an electrcal fault with an operating solenoid if you like but i would change fluid first it might have never been changed before