Sonata 2001 GLX automatic box problem

Hello and greetings to all in the forum.

I present my problem with a Hyundai Sonata GLX 6V year 2001 and is as follows:

the automatic box -4 speeds- is operating in 2nd speed all the time. I have already scanned it and shows no electrical failures. Sometimes it begins to change well - it does all the perfect changes - but only for one or two days, and then return to the same problem of not changing 2nd. speed ... some track. Thanks advanced and greetings. Vicente

There are 2 things: scan the vehicle when you fail and without turning off the vehicle because someone may have changed the battery voltage to ignition to erase the memory of the ECU when turning it off. The other thing that has happened is that when a vehicle stops making changes and does not give fault codes and I mean any not only those of the transmission is because the TCM or the PCM if it is integrated into the same transmission and engine computer is protected by mistake and would have to change the computer. But the best thing before changing is to check everything and sometimes as I spend with a versa that does not codes with a generic scanner does not mean that sometimes there are codes that only with a specific scanner of the brand you can see some fault codes. In the North American Versa if you do not have the brake light fuse does not make transmission and code only appears with a specific scanner for Japanese with the ORTOS says no faults detected.

Hi Choto thank you very much for your information, I will review the points you indicate and I hope to find the fault. Receive a hug and good luck.