Toyota iQ Fog Sensor Problems

Sounds like the fog sensor is indeed the culprit. The air conditioning, spray nozzles and mirror heating are often linked to the climate control system, which relies on that sensor. Have you tried looking at the sensor itself? It's usually located near the rearview mirror, behind the plastic cover. Maybe the connector is loose?

I haven't actually seen the sensor itself. Where exactly should I be looking, and what am I looking for? I'm not really sure what a fog sensor even looks like, to be honest.

Okay, so the fog sensor detects humidity and helps control the climate. It's small, usually a black plastic box. Given all those symptoms, and without being able to physically check it myself, it's likely a wiring issue. A defective cable or plug connection could cause all that. Honestly, with all those systems affected, it might be best to get it checked by a workshop.

Thanks for the advice! Turns out you were right. Took it to a shop, and it was a corroded connector on the fog sensor. They cleaned it up and charged me 95€. Everything's working again now!