Transmission problem

problems with my transmission. When I am driving down the road everything is fine, until I will feel a small jolt, and my check engine light comes on. When I came to a stop my transmission will not downshift back to first gear, I have to manually shift by using the sport shifter. The problem is that I can't shift it to first, it will only shift to second gear. When I am at a higher speed the transmission will not shift to fourth gear, I can not manually shift to fourth either, only second or third gear. I called the Kia U.S. Motors and talked to there Mechanic but they could not tell me what is wrong. Please help me.

If it was my Kia and I wanted to find the problem before real damage was done. I would find a good Transmission repair shop and have them tell you whats wrong and what it will take to fix it.

Sounds like an Input Speed Sensor. Same thing happened to my same model/same year Optima. The reason it drops down to 3rd is a failsafe since the the sensor can't tell the computer or whatever when to shift. So it will only do