S60 Oxygen Sensor Faulty Cable

Sounds familiar! I had a similar issue with my 2016 Opel Astra: check engine light, higher fuel consumption. It was a faulty oxygen sensor. Did you check the sensor connections for corrosion or damage?

What specific areas should I inspect for potential corrosion or damage on the sensor connections? Are there particular components or wiring harnesses known to be more susceptible?

Give the connector a good look – unplug it and check for any green gunk or broken pins. Trace the wiring back a bit from the sensor; sometimes the insulation cracks and causes shorts. If you're not comfortable with electrical work, take it to a workshop. Better safe than sorry with the catalytic converter and exhaust system.

I had it inspected. Diagnosis confirmed a defective oxygen sensor due to a faulty cable connection, as you suggested. The repair, including sensor and wiring replacement, cost 95€.