Insignia O2 sensor fault

The O2 sensor issue on the Insignias is fairly common. Given the mileage (93177 km!), it could just be aged. Have you noticed any exhaust smell or performance issues besides the light and fuel consumption? A faulty cable or plug connection to the sensor is definitely a prime suspect, but the sensor itself might simply be on its way out. Which sensor is the error pointing to – pre-cat or post-cat?

Good question about pre-cat or post-cat – I honestly don't know! Is there an easy way to figure that out without taking it to a mechanic? Also, no noticeable exhaust smell or performance dips, just the light and the thirsty engine.

If you don't have a code reader, it's tough to say definitively which sensor is throwing the error. Since you are not experiencing driveability issues, I would suggest you visit a local workshop that can read out the error memory for you and properly diagnose the failing part. It might very well be the cable, but it can also be the sensor itself. If it is 'just' the cable or a defective plug, this can be sorted out fairly quickly and for little money. I would budget around 95€ for parts and labor.

Thanks a bunch for the advice! I took it to a local mechanic, and it turns out it was indeed the upstream O2 sensor. They replaced it, cleared the code, and the check engine light is gone! Fuel consumption seems to be back to normal, too. Really appreciate the help!