Since I've been a member of this forum, I've asked y'all over and over again how to fix this issue. Today, I would like to leave you some help from my side as well.
P0455 code as read by the OBD2 scanner is a large leak detected in the EVAP system. Since GM decided to mount these sensors in the un-protected areas like underneath the vehicle in this case, they do tend to go bad.
While searching for parts for this issue, you will find that Dorman as well as ACDelco makes these parts. The vent control valve which needs replacing at this juncture is mounted in front of the charcoal canister. The charcoal canister is a $220 part at many online stores. Dealer is higher.
So the vent control valve mounted in the 2010 Cadillac SRX has been redesigned by the manufacturer so if replacement is necessary, in my case it is, the vent control valve is readily available in Auto Zone etc (special order/not stocked) but GM notates IT NEEDS TO BE REPLACED WITH A NEW HARNESS.
I am leaving y'all the part numbers and prices of the same should you need it. Merry Christmas 2018!!! :-)
AC Delco Vent Control Valve: Solenoid $52.21 at any GM dealer Part # 13575702 or CHEAPER online/ I got mine for $25 at Cardit.
AC Delco wiring harness part number: 20922087 $62.00 Dealer item only.