Volvo Repair: 2001 Volvo s40 1.9 turbo, 2001 volvo s40, vadis system

Question
I have cam position sensor error  (I threw the reading out but it think it said P015) which is preventing me from getting an emissions pass on inspection.  I've read a few forums on this problem and the advice seems wacky, e.g. replace your oil with 5W30 instead of 10W30 or use 89 octane instead of 91 octane or vice versa.  My repair shop says that the next step is to replace the cam position sensor which might but not necessarily fix it.  I tried to see it but am not sure--is it on the top rear of engine on the driver's side and should I do the replacement?

Answer
Duncan, not sure why that would fail an emissions test but anyway, I would go to a real Volvo Shop and have them hook it up to the VADIS system.  This PO 9837338383 stuff really bugs me.  I would replace the sensor if it was a hard code permanent fault but obviously the car is still running.  Have it checked out.  Roger