I had a similar problem with my S60. The dealer replaced a part - some kind of relief valve, I believe - under the CPO warranty. It was three years ago, so I can't remember all the details. They had to remove the fuel tank to do it, after removing the custom trailer hitch that was in the way. No complaints, they just needed to re-schedule the work because the hitch R&R was going to add time to the job. Only cost me the deductible, and the warranty also paid for a rental car.

CPO covers EVAP system as part of the pollution control devices. A major leak could be the gas cap, but is probably a plastic elbow next to the fuel filter and rear wheel.
Your car is a Volvo CPO, call the service people and ask them if it is covered. They don't need to service the car before answering the question.
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My name is Klaus and I am a Volvoholic.