Mistra oxygen sensor issue

That sounds frustrating! Increased fuel consumption and a check engine light are annoying. Since you've checked the connections, it could be the O2 sensor due to a defective cable or plug connection. They're crucial for the air-fuel ratio. Is the car running rough, or just drinking more fuel? Any difference in how it idles? Think of the sensor as the conductor of your engine's symphony. If it's off-key, the whole orchestra sounds bad!

Good analogy! The car seems to idle fine, no weird noises or vibrations. It's just thirsty, really thirsty. If the sensor's gone bad, can I fix it myself, or do I need a mechanic? Can I still drive it, or will I fry the catalytic converter?

Okay, the fact that it idles okay is good, lessens the chance of it being catastrophic. Given the symptoms, and the fact that fiddling with the connections didn't help, an aging O2 sensor with potentially defective connections is highly probable. Driving with a bad O2 sensor can damage the catalytic converter over time due to an incorrect fuel mixture. You could try replacing the sensor yourself if you're comfortable with car maintenance, but for the sake of the catalytic converter, I'd suggest getting it checked by a workshop ASAP. It is like ignoring a small leak in your house, it might cause serious problems later on.

Roger that! Thanks for the advice, really appreciate it. Dropped it off at the shop, and you were spot on – faulty O2 sensor with a bad connection. Cost me 95€ to get it sorted, which is a lot less than a new catalytic converter. Crisis averted!