For the last few weeks I've been experiencing problems with my 03 Tiburon gt automatic. I bought the car this past February and it has about 115,xxx miles now. I noticed a few weeks after I bought it that sometimes the cruise control would cut off and the speedometer would fluctuate or not work at all. It would happen only once every few days or so. Over the last few months it increased to a several-times-a-day everyday problem. A few weeks ago I was driving on the highway and the car suddenly jerked and knocked itself into third gear. It stayed in third gear until I restarted the car, sometimes even then. I haven't driven it since except for trying to fix the issue. I had the codes ran on the car and it came back with p0715, p1529, and p0720. I know these are the codes for the input/output speed sensors and then the tcm code for the check light. I have replaced both sensors and checked the wires, however the problem persists. I've noticed that when the old output sensor is replaced with the new output sensor, the car no longer tries to stay in third gear but it actually wants to stay in first. It does not want to shift out of first and only does so at high rpm using the slapshift into second. It still does the jerk from gear to gear. When the new output sensor is then again replaced with the old, it goes back into third (limp mode). It is still pulling those same codes as mentioned earlier. What could the problem be?

 

ignoring the error codes for a second, those symptoms correspond with a bad speed sensor. speedo gets signal from the transmission for your gauge, cruise gets signal from that as well. if its not a proper signal it just cant make sense of it and turns off. same with the shifting problems, if the TCM (transmission control module) can't get a reliable signal, it can't control things properly.

if you have replaced the sensor and verified that it works, i would start looking at the wiring (start with connector) or bad TCM. i'm pretty sure that the TCM is separate from the ECU, but i could be mistaken. im sure someone will come along and slap me upside the head if i'm wrong.

also please reference your error codes on www.hmaservice.com. that site will give you full instructions on how to troubleshoot and fix the problem. you must use IE, sign up for a free account/login and download the adobe plugins under site requirements.