XC70 Control Unit Malfunction

Those symptoms really suggest a control unit problem. Implausible programming can cause a lot of errors. Have you checked for software revisions or tried a system reset? Also, did you use an OBD tool to get the specific error codes? Knowing those codes will help find the cause. A faulty or old software version would be my first guess.

I haven't tried any software revisions or resets myself. I don't have an OBD tool. Would a simple control unit recalibration fix this, or is something bigger likely needed?

Recalibration could work, but it's risky. Given the errors and no diagnostic tools, I wouldn't try fixing it yourself. You could make it worse. I'd take it to a Volvo workshop. They can check the control unit and reprogram or repair it. 240€ sounds fair for a recalibration. The technician can confirm if that's all it needs.

I took your advice and went to a Volvo shop. They confirmed the control unit needed recalibration, and that fixed the software and other problems. Thanks!