It's not too hard.

Clearance to the firewall is tight. You may need a light & mirror, but you can get the screws by feel fairly easily. You might also get a 1/4" hex drive Torx bit for the pan head screws. I think the size may be T-40. Also, a 1/4" ratchet box end wrench is handy for these tight clearance situations. Snap On makes a 1/4"-5/16" wrench like this that's not too high in price. You use this with the short 1/4" hex drive bits.

Once you get the cover off, you've got the sensor part. There is also a metal rotor on the Exhaust cam, but you may not need to take that off.

If you've got leaky heater hoses back there, you should replace those. Leaks in the cooling system can result in extremely costly problems if you drive with the coolant level low. One should NEVER do that.

The Volvo replacement hoses are around $52 for the pair. This also includes the short one that goes on the other side of the heater valve, which you cut off of one end of one of the hoses.

I wouldn't go with aftermarket on those hoses.