Volvo V50 O2 sensor error

Sounds familiar. I had a similar problem with my old Peugeot 307. Check engine light, increased fuel consumption, and O2 sensor errors. In my case, it turned out to be a corroded connector on the sensor wiring. The sensor itself was fine, but the bad connection was messing with the signal. Have you checked the plug itself for corrosion or damage? Sometimes a bit of contact cleaner can work wonders.

Cheers for the tip! I did give the plug a quick once-over, but I'll take a closer look for corrosion. When you say corroded, are we talking green gunk or something more subtle? Also, did you manage to fix it yourself, or did you take it to a shop?

Yeah, I'm talking about that greenish/white powdery corrosion. It can be subtle at first, just a bit of residue. I tried cleaning it myself, but the error kept coming back. Eventually, I took it to a workshop. They replaced the connector and re-terminated the wiring. Problem solved. Given the age of your V50, it's a pretty common issue. But better have it checked correctly.

Right, I'll give the connector a proper inspection, but it sounds like a trip to the mechanic is on the cards. Thanks for sharing your experience; it's good to know what I'm potentially up against. The car is back from the shop, and a defective cable or plug connection was the root cause! Cost me 95€.