Sienna Fog Sensor Error AC Issue

I had a similar problem with my Sienna. The symptoms you describe sound very familiar. Did you check the relevant fuse?

Which fuse are you referring to? I checked the main fuses, but I didn't see anything obvious.

It's difficult to pinpoint the exact fuse without a diagnostic scan. However, given the interconnected nature of the systems affected (climate control, mirror heating, windshield defogging), it is highly probable the Body Control Module (BCM) is involved. It might be related to the humidity sensor circuit, a common cause for these electrical gremlins. To avoid making it worse, I would advise against extensive DIY troubleshooting and recommend a visit to a trusted workshop. A diagnostic scan should swiftly identify the malfunctioning component and confirm the appropriate remedy.

Thanks for the advice. I took it to the workshop, and it turned out to be a defective connector, just like I suspected. The repair cost 95€, which seems reasonable.