Check Engine Light = Valve #4 Problem

I was told by my local Volvo service department that the Check engine light is due to Valve # 4 being burnt and problems with valve # 4. They told me I should fix the problem and it would cost about 3,000 dollars. Now the car runs fine, I don't see a difference in performance. They reset the light and said that the light will come on in three days. The light did not come on for a week and then it went out the next day. It keeps doing this. But so far the car runs well. I took to a local volvo mechanic and he test drove it and said that the car has no problems and that I would have notice a performance and noise.

Could this be a computer problem? Has this happen to anyone else? Who can I complain to at Volvo? I have sent an e-mail to them and no response.

CAR:
Volvo v70 T5 2002
Manual
57,000K

Thanks