S80 reduced engine power error

I understand your frustration. A defective engine control unit can certainly cause those symptoms. Before jumping to conclusions, have you tried a system reset? Sometimes, a glitch can trigger these errors. Also, could you provide the exact error code stored? That might help narrow down the potential cause.

Thanks for the quick reply! I did try resetting the system by disconnecting the battery for a while, but the error and reduced power came right back. Unfortunately, I don't have the exact error code written down. Is there anything else I can try myself before throwing in the towel and heading to the workshop?

Given that a system reset didn't resolve the issue, and the symptoms persist, it's highly probable that there's a hardware problem with the engine control unit or its associated components. While further diagnostics might pinpoint the exact fault (perhaps a defective main relay, which is a known issue), this requires specialized equipment. I would recommend taking it to a workshop equipped for Volvo diagnostics; they can perform more in-depth testing to confirm the fault and provide an accurate repair solution.

Okay, thanks for confirming my fears! I bit the bullet and took it to a specialist. Turns out you were right, it was the main relay causing the ECU to go haywire. Cost me 120€ to get it sorted. Appreciate the help!