Manual gearbox jammed

Over drive lamp fails. I guess or is it flashing for errors.
the service manual covers all that , buy it and read ?
problems with 4R70e transmission , not told. clearly
scanning the PCM now is what is best done.
any time a transmission like this fails to shift the PCM tells you why or how it was detected. via what. with DTC codes
why not scan it.?

OD function. real name is 4th gear is overdriven
so if the tranny stops at 3rd gear we say 4th gear is dead.
4th gear is 0.70: 1 ratio.
engine spins 3/4 turn(near) and drive shift goes 1 full turn
as in overdriven gear.
now lets talk dead 4th gear, all the ways it can happen
sadly lots. for sure you not scanning the PCM first to see why.
speed sensors lie
transmission sensor shows overheating,
engine load is too high. 4th gear makes that worse so why wreck clutch packs doing that and it sure does not.
learn the transmissions are shifted by speed and loads.
load on the engine if tops.
VSS errors, OSS errors
and more, even a weak engine, is a cause.
sorry but this is how it all works
and you can not fix modern cars and trucks lacking a good scan tool..

The detent on the shifter for 4th is worn. Worn thrust washers on the gear shaft can also cause this.

This button only makes the gearbox change from 3rd to 4th or 4th to 3rd, will not down shift in any other gear, make sure it is in 4th gear, usually above 60km, than press o/d off it should go into 3rd gear, if it does not than see a automatic specialist, it is usually a sensor, if you go to Toyota they will charge you a fair bit.

if a manual gearbox then check the oil level in the gearbox ,it has to ba newer model because the old minis used the engine oil in the gearbox as it was all in one

your synchro ring is inside the gearbox and you are going to have to remove the gearbox and open it up to replace it,but its best for a mach how is expirinsed to do it

an evn better fix if its playing up is to fit a manual gearbox

im not telling you what to do because it could be a bad transmission and an easy fix but I cant tell without looking at it , but if its a hard fix just go to a reliable junkyard and get another

did you change your clutch when you changed your gearbox??? also check the clutch master cylinder.

There are four probable causes when the gear is stuck in one position, and they are precisely explained in this handy diagnostic article that I know will help narrow down the culprit of your difficulty:
http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Vehicle_Car_Zone_Cars_Trucks_Vans_Transmission_System_Stuck_In_One_Gear.htm

Good luck!
Brad

i suspect the modulator might be faulty and mayby
trans. filter would need replacement