Lexus IS Temperature Readings and CEL

I had similar symptoms on my IS. Have you checked the coolant level? Low coolant can cause all those issues you're describing. Also, is the radiator fan running constantly or not at all? That could point to a faulty sensor or relay.

Coolant level is fine, checked that first. The fan seems to be behaving normally, cycles on and off as expected. Where exactly did you experience the sensor issue? Was it throwing a specific code, and was it related to the cooling grille itself?

My apologies, it wasn't a sensor issue in the end, I just remembered the symptoms were similar. I'd get it checked out by a workshop if I were you, the cooling system on these cars is complex and could be a number of things.

Thanks for the input. Took it to the shop, turned out to be a blown fuse for the grille shutter system. 52€ later and it's all sorted.