HI Smoke test done by a mechanic and there was no obvious visible leak detected however he tested newly changed vent valve and was adviced to replace it with original GM part as did not close as commanded by his OBD tester unit so I did replaced it with original part but he code P0455 came back after 48 hours. Another mechanic suggested that I should change the purge valve. Since purge valve is very easy accessible then can somebody tell me how to test it
Thanks a lot