Check engine light is on. I've been told turbo. Runs great how can I b sure

CHECK HOSES, VACUME LINES, THE BLOW OFF VALVE VACUME LINE OR TAKE A VACUME GUN AND HOOK IT UP TO YOUR BLOW OFF VALVE AND SUCK IT DOWN, IF THE THING DONT SUCK DOWN AND HOLD NEGATIVE VACCUM THEN THE DIAPHRAM IN THE BLOW OFF VALVE IS BAD THEN REPLACE THE VALVE, TURBOS ARE PREATTY TOUGH AND NOT MUCH TO GO WRONG, THEY HAVE TWO BLADES ON A SHAFT AND THEY RIDE ON A BEARING, AND NOT THE KIND OF BEARING THAT HAS BALL BEARINGS,THE SHAFT SLIDES INTO TWO BEARINGS, NOE AT THE EXHAUST OUT LET AND ONE AT THE INTAKE END OF THE TURBO,IF THEY WARE OUT, YOU GET EXSESIVE OIL IN THE INTAKE SYSTEM, AND YOUL HEAR THE BLADES RUBBING IN THE TURBO HOUSING, ANOTHER PROBLEM WITH THESE VOLVOS THAT PUTS OIL IN THE INTAKE SYSTEM AND STARTS PUSHING OIL OUT SEALS AND SOFORTH IS THE PCV SYSTEM PLUGING UP, THEIR IS A BREATHER BOX UNDER THE INTAKE MANIFOLD AND ITS A PAIN TO DO BUT IF YOU HAVE ALOT OF MILLAGE AND THE OIL CHANGES HAVE BEEN NEGLECTED THEN THIS IS PROBABLY PLUGED UP, TAKE OFF THE OIOL CAP AND LOOK UNDER IT, IF IT LOOKS LIKE WATER OIL MIX THEN ITS DEFFINATLY PLUGGED UP AND NEEDS IMIDATE ATTENTION. THEIR IS A AIR PUMP UNDER THE FRONT HEAD LIGHT ASSEMBLY, AND A VALVE JUST ABOVE IT THATS ROUND WITH AN ELECTRICAL PLUG IN THE SIDE AT THE TOP, A VACCUM HOSE GOSE OFF THAT TO YOUR PCV SYSTEM, THAT VALVE CAN GO BAD, THE SWITCH IN IT OR THE RUBBER DIAPHRAM. THESE ARE THINGS TO KEEP AN EYE ON VOLVO TOLD MY FRIEND IT WAS HIS TURBO, NOT EVEN CLOSE, THEY WANTED 2700.00 AND THEN WHEN THEY ARE DONE IM SURE THEY TELL HIM ABOUT THE PCV BOX BEING PLUGED UP. HE DIDNT WNAT TO SPEN THE MONEY, SO NOW IM A PROUD OWNER OF AN XC70 TURBO, AND NOTHING WRONG WITH HIS TURBO LIKE I SAID...IT WAS THE BREATHER BOX PLUGED UP.