Volvo: 99 V-70 fault code PO455, o2 sensor, rear brakes

Question
99 V-70,I just had a lot of work done to my car,re-built abs installed,new map sensor,new o2 sensor,rear brakes,2 new coil packs,new plugs.I had no warning lights for 2 weeks.Check engine light came on,I had auto zone read code,PO455,I replaced broken pre-heater hose.Light went off for 3 days.Now light is back on.What else should I check?

Answer
Cindy,
That fault codes means there is a major leak in the fuel tank emission system. That will require testing the system for leaks, by applying pressure or using a smoke machine. There could be a bad hose or line or even a loose gas cap or bad seal on the cap.