Picked up a 2017 suburban ls about a month ago. Got the p0455 code. On all my past trucks, that code means the gas cap is leaking. Only issue 2017 suburbans dont have gas caps. They have a self sealing thing already built on. Are there issues with that and how do I fix it?

Thanks

 

P0455 is EVAP leak. It doesn't necessarily mean the gas cap. It could include any of the other components (hoses, canisters, valves etc.)

A smoke tester might be a good start.