Adam Incorrect Temperature Check Engine Light

The symptoms you describe could indeed point to a cooling system issue, possibly related to restricted airflow. Has the vehicle's mileage exceeded 100,000 km? Has the radiator grille been visually inspected for any obstructions?

Yes, the mileage is currently at 124020 km. I've checked for obvious obstructions like leaves or debris, but found nothing. Could it be something internal, like a faulty thermostat?

While a faulty thermostat is possible, the incorrect temperature readings and slow warm-up, along with the check engine light, strongly suggest a cooling grille issue impacting overall engine temperature regulation. Consider having the system professionally diagnosed, since it is possible that there is a defective fuse. You want to prevent potential engine damage. A workshop visit is highly recommended.

Thanks for the advice. I took it to a local workshop, and you were right. Turns out a fuse related to the active grille was defective. Repair cost was 52€. Everything seems to be working fine now.