2001 Hyundai Accent Auto 1.6
This problem happened out of a sudden, before that it was shifting fine. One day while driving on the highway, the transmission just downshifted by itself and I am no longer able to shift it pass 2nd gear. I had the car tow to my house, started it the next day and found out that reverse is gone. It acted like it was just in neutral.

Went to the junkyard and found myself a used transmission. My mechanic friend helped me put on the transmission. Many hours later, found out that the old problem still persist. No reverse and no third gear. O/D switch is working and L, 2 and D all working.

What are the odds that both transmission have the similar failure?
Or can it be something simple like electrical, sensor or fluid problem?

Please advice. 3 weeks without a car now.

Thanks

I have the same problem and same car (140K). I swapped the transmission computer, fluid, and kickdown solenoid. I also have a used trans from a 2000 1.5L (same trans computer and maybe software??) which has lower gearing. I am in the process of installing it. Your used trans makes be think it is the solenoids or some stripped spline referred to in another post. Some claimed that a speed foam was used from NAPA (maybe equivalent to BG trans cleaner, noting that you use at your own risk) to clean the tranny sludge and etc. These are just other posts I have found. Any comments? Trans kits are $100-$200 without hard parts? If you have 2 trannies you can rebuild one. Be sure to flush the radiator oil cooler section (maybe let soaking the BG/Speed or carb cleaner, my idea) per trans mech. FYI

Also replaced the speed sensor (a cable with 2 sensors on top and bottom of trans) and cleaned contacts. Maybe your problem might be the wiring harrass if not the same problem on both trannies.