Won't go into gear after oil change - 2001 Isuzu Trooper

Your speed sensor might be hanging up.when you changed the trans oil and filter did your old oil smell burnt, and make sure you put the right fluid init.If your oil is burnt looks like you have a big job ahead of you.

If it goes into other gears correctly, then the issue is likely a synchromesh problem with that particular gear, and the gearbox may have to be stripped.
You may try changing the gear oil first though, as this can often fix the issue without having to spend too much money on unnecessary repairs.

It might be.
You should first change the gearbox oil and replace the gearbox oil filter, then retry.
If you are still having an issue, then check the vehicle's speed sensor and TCM.

Try cleaning the MAF sensor. Computer uses that info to determine pump pressure. If that doesn't work, you're looking at a new tranny

Done cars have a kill switch if they are low on oil. Check your oil. If the oil is good, it may be the ignition switch.

You probably won't find one. In an automatic transmission you cannot just simply remove gears or change the selector fork (especially because there isn't one). Everything needs to be there or it won't work at all.

Change the gear oil. If the gear oil is leaking get it fixed as soon as possible. If all the oil has leaked then it may have severely damaged the gear box.

had same problem advised to change pump which i did solved problem for two weeks now no gears will select

sounds like the selector box at fault but change the auto oil and filter with some treatment and this should solve youre problem

tranny shop time tranny pump problem