Hyundai Repair: 2000 Hyundai Sonata, transmission control module tcm, transmission control module

Question
I have a 2000 Hyundai Sonata 2.5L V-6. My check engine light has come on and my car has lack of power at low speeds and does not shift. When going into reverse or drive sometimes the car jumps. As I am accelerating, the rpms go up with the speed but only drop down when my speed decreases. I have taken it to Aamco and they said it is an internal problem and want $995 just to pull it and check it. I have it checked at a local auto parts store and it came back that my O2 sensor, TCC solenoid valve, and ATF Temp sensor need to be replaced. Will replacing these things fix the problem???

Answer
Most auto parts personnel aren't qualified to determine what needs to be replaced by reading a diagnostic trouble code (DTC).  In most cases, this is because DTCs do not indicate a failed component, but rather a reading from a sensor or actuator that doesn't fit what the engine control module (ECM) expects.  The problem causing this discrepancy can be in the sensor that provides that signal, the wiring, or the computer.

Just based on your symptoms, it sounds like your transmission control module (TCM) is seeing something it thinks is incorrect, causing it to put the transmission in 3rd gear at all times and request the ECM turn on the check engine lamp.  

It's unlikely that replacing the listed components will resolve your issue.  The oxygen sensor will rarely result in a performance issue, and the problem with the TCC solenoid valve and ATF temperature signal may be with the wiring rather than the sensor and solenoid themselves.  Nor do I think that AAMCO will be able to give you a better answer by removing the transmission.  

What I do need to assist you further, however, is a listing of the actual diagnostic trouble codes.  Obviously, the guy at the parts store read the codes with a scanner or code reader, but what he's done is to provide you with an explanation of what he thinks needs to be done rather than provide you with the codes themselves.  The codes will each have five charaters; in this case it will be the letter P followed by four numeric digits.  These codes will give me the best information about what the computer has seen that isn't normal.