Hyundai Repair: 01 Sonata Output Speed Sensor, output speed, speed sensor

Question
For the last month and a half or so my 01 Sonata has had some transmission issues, as Im driving along at random times my RPM would suddenly rev real high and my car would suddnley jolt or kick out for a second, after it jolts it still moves along ok, but when I come to a complete stop at a red light or a stop sign or whatever and go to take off again I loose 90% of my take off power, with my pedal to the floor it takes off super slow until I get going to about 20 or 25mph or so and then it drives fine again. Some times it jolts very softly and sometimes it jolts really hard. Now when I shut my car off and turn it back on it seems to work and takeoff just fine until the next time it randomly jolts again and then its the same ol problem again. Sometimes it takes 30 seconds sometimes it takes 40 minuites before it randomly jolts. I had a computer scan run on the car today and there was a transmission code that popped up for the output speed sensor circut. In your professional opinion dose an output speed sensor sound like it could be the guilty culprit for my problem? My speedometer reads just fine? I also had a misfire code on cylnder #4 witch I will replace the plugs and wires to take care of (there overdue for that anyway) And there were 2 other codes that they had no clue what they ment.

U3118 and
C307

If you could tell me what those codes mean I would greatly appreciate it.  

Answer
The symptoms you describe are exactly consistent with a faulty output speed sensor.  The TCM (transmission control module) receives data from the input and output speed sensor of the transmission (as well as other data) and uses those data to determine when and how to shift the transmission.  If it doesn't receive the proper signals from the speed sensor, it'll put the transmission in third gear and leave it there until the vehicle is turned off and restarted.  If you've got code P0720, don't sweat putting the sensor in.  I've seen many cases of this and only one where it wasn't the speed sensor itself.  The reason your speedometer reads fine is that the output speed sensor (located directly over top of the transmission output shaft) sends data to the transmission computer only.  The instrument cluster receives vehicle speed from the vehicle speed sensor which mounts on the differential of the transmission.

I don't show any data on a U3118 or a C0307 on any Hyundai vehicle, so there's probably some sort of communication issue with your scan tool.  U codes indicate a controller network communication problem, and Hyundai doesn't use U codes for your car.  C codes indicate a brake/traction control issue, but all would be C plus four digits.  I stuck a zero in front just to do a search and see if anything came up.  If your ABS and TCS are  working normally and the ABS and TCS lamps don't come on when driving under normal conditions (ABS and TCS aren't activating), then don't sweat the C code.  If you don't have ABS, it's not even possible for you to have a C code.