Volvo: 644A EMISSION SYSTEM SERVICE REQUIRED, volvo s80, camshaft position

Question
Dear Sir,
I have a VOLVO S80 T5 turbo 2.0 ltrs and I replace the timing belt before a week in VOLVO workshop in my country.Next day I used my car the engine lamp on and notify me that :EMISSION SYSTEM SERVICE REQUIRED.I took it back and the computer show us that the camshaft position it was +10 degrees instead of (+)-8 that has to be in normal position.They told me that I have to replace the variable but I don't trust them.I took the car in a friend of mine and show us the code :644A CAMSHAFT SENSOR WRONG POSITION.
Please help me what it can be the problem of my car?This was  a mistake of the mechanic in the workshop during replacement the timing belt?
Waiting your soon reply

Best Regards

      Nicolas

Answer
Nicolas,
Most times that means the cams and crank timing marks were not set properly and the VVT is out of sync. Sometimes the VVT can be reset, but not always sure if that will work. That is possibly why they recommend a new one. To reset you need to follow the procedure for your engine to set it to TDC. Pull off the belt remove the rear cam plug and the cam sensor use the special tools to hold the cams in the number one position and either install a new VVT or if yours is one that can be reset do so. Resetting them is a unusually procedure. You will need access to a manual for your engine.