+1 for possible fuel powered heater
My 2009 XC90 D5 diesel has one
Sometimes - and only sometimes - it smokes a lot.
You'd think the car was on fire when it happens!
And when it happens, if you roll to a stop you can see the smoke rising from around the engine bay.
On my D5 XC90 the fuel powered preheater exhaust is under the front left-hand bumper, you can hear the fans kicking in to exhaust the combustion chamber before it fires up, and once running starts to sound like a mini jet engine. And it blows out hot exhaust as well, of course.
The 2016 V90s have them, see here:
https://www.volvocars.com/uk/support...-driven-heater
The manual says the heater is the right hand wheel housing, which will be front wheel housing, likely behind the front bumper.
To confirm if yours has one, look for the sticker on the fuel filler cap. The 3 x wavy arrows pointing up (indicating heat rising) means the car is fitted with the fuel-powered heater.