Moe, there is a leak in the line. Somewhere. Wether it is a cracked plastic elbow or a stuck valve or a bad relay, the solenoid cannot close properly which triggers the P0440.

This is the bane of errror codes. Multiple reasons can cause the same error, just like vacuum leaks will mask an O2 sensor problem or be the cause of it. The only way a car company could be more specific is to have sensors everywhere and then they would need to install sensors for sensor failures. Kinda like NASA.

You need to pull off the right rear wheel and check the cannister line elbow. If it looks to be good, then check the cannister connections in the left front of the car, then check the check valve, then...

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.