Harsh Transmission Shifting

Hey everyone, I had my transmission rebuilt a little over a year ago on my 1999 Kia Sephia. It is a 4 speed automatic transmission. I had opted in for the 3 year warranty.

What seems to be happening is that whenever I accelerate at a normal speed there is a harsh shift/jerking from 1st to second gear. I do not experience this with any of the other gears or during quick accelerations. I had noticed this a bit before but it never seemed to be bad and when I took it to the shop they said it seemed to be functioning normally.

I took it back to the transmission shop today and gave them specific instructions when giving it a test drive so they know what I am talking about. They came back to me and told me that they think its a dirty speed sensor that may need to be replaced.

I do not get any check engine lights and no other warning lights on my dashboard are lit, and it doesn’t sound right to me that this would be caused by a speed sensor.

I was just wondering if I have good reason to be suspicious of what they are saying or if anyone has any ideas.

Thanks again!


I wouldnt be suspicious at all about a speed sensor malfunction causing the harsh shifting. What happens is the computer uses inputs from different engine and transmission sensors to control shifting and line pressure inside the transmission. If one or more of those sensors become faulty and give the computer false information, the computer will place the transmission into limp mode. When in limp mode, the computer maxes out line pressure inside the transmission to protect it from destroying itself. A faulty speed sensor will definately put the transmission into limp mode and max out the line pressure. This would make you feel the harsh shift.