S40 oxygen sensor fault

I have an S40 too, and I had similar issues a while back! O2 sensor was throwing codes, and my fuel economy was terrible. Did you check all the wiring thoroughly? Sometimes it's a pain to spot the exact break or corrosion.

Cheers for the reply! I gave the wiring a good once-over, but honestly, it's hard to be 100% certain without proper testing equipment. Did you manage to sort it out yourself, or did you end up taking it somewhere?

I messed with it for a bit, cleaning contacts and all that, but in the end, I just took it to a workshop. Turned out the sensor itself was kaput; they swapped it out, and all good. Cost me about 95€, sensor and labor included.

Thanks a bunch! Sounds like I'm heading for the workshop then. At least I have a better idea of what to expect. Hopefully, it's just the sensor. Fingers crossed!