President O2 sensor issue

I had a similar issue with my Nissan (though it's a newer model). Same symptoms: check engine light and guzzling fuel. The O2 sensor error could be a faulty sensor, sure, but did the OBD reader specify which sensor? There are usually a couple, before and after the catalytic converter. Knowing which one will help narrow things down. Also, have you checked for any exhaust leaks? That can mess with the readings too.

Good point about specifying the sensor - I should have mentioned that. It's indicating the pre-cat O2 sensor. I haven't specifically checked for exhaust leaks, but I don't hear anything obvious. Where should I be looking?

Okay, pre-cat sensor. Exhaust leaks can be tricky to spot just by sound. Visually inspect the exhaust manifold and the pipe leading to the catalytic converter for any signs of soot or damage. Honestly, though, given the age of the sensor and the error code, plus your symptoms, it's pretty likely the sensor itself. If the wiring looks good, I'd probably just bite the bullet and replace it. Taking it to a workshop might be the easiest solution and they can properly diagnose it.

Thanks a lot for the advice! I took it to a local garage and you were spot on. They checked the wiring and confirmed it was fine. Replaced the pre-cat O2 sensor and cleared the error code. Runs like a charm now, and fuel consumption is back to normal. Total cost was 95€.