Volkswagen: Checking engine light alert, mileages, problem thanks

Question
I have an used 2000 volkswagen wagon GLX car (mileages is about 110,000. The checking engine light and the Emission Workshop alert come on.  It has the 2.8 liter V6 engine.  First a repair stuff help me to  turn off the light. While after driving about 60miles, it appears again. During my driving I can not feel anything. But from low speed to high speed, I can hear a scream sound. During the stable speed driving, it seems OK. What cause this problem?

Thanks  

Answer
Sorry for the late response.  There are lot's of reasons why the check engine light an come on.  It just means that the ECU had bad readings reported to it by one or more of the many sensors.  Do you have the codes that were read from the ECU?  If its P0421 and P0431, this is caused by a threshold error in the ECU and can be fixed by reflashing the ECU.