C8 Coolant Loss

Sounds familiar. I had similar symptoms with my 2012 Opel Insignia, also gasoline. Low coolant, check engine light, and an error code. Have you thought about air pockets in the cooling system? They can mess with the coolant level readings and trigger those symptoms. Is the engine temperature higher than usual? That could mean overheating from not enough coolant.

Thanks! I hadn't considered air pockets. How do I check for and get rid of them? Also, could a small coolant leak, maybe from the water pump or a hidden hose, slowly drain the coolant without being obvious?

To bleed air pockets, look for bleeder valves on or near the thermostat housing or radiator. Open them while the engine is running to let the air out, but be careful, the coolant might be hot. A small leak is also possible. Since you can't find a visible leak, get the system pressure tested by a mechanic. They can pressurize the system and look for pressure drops, which would show even a tiny leak.

Thanks for the advice! I booked it into a workshop, and it turned out to be a small leak in a radiator hose. They replaced it, and the total cost was 52€. Your suggestion to get professional help sorted it out quickly.