Altima Fog Sensor Issue

Sounds like a bad fog sensor, alright. If the ECU thinks it's foggy, it'll disable the AC and other features to prevent further windshield fogging. Have you checked the sensor itself and the wiring harness for any obvious damage or corrosion? Also, are you sure the refrigerant level in your AC system is OK? A low charge can sometimes cause weird climate control issues. The mirror heating might be part of the same circuit, or it could be a separate issue.

Good point about the refrigerant level - I hadn't considered that. Where exactly is the fog sensor located? I've been poking around the dash but haven't spotted it yet. And you mentioned checking the wiring harness - any tips on what to look for specifically? I'm not exactly an expert when it comes to electrical stuff.

On your Altima, the fog sensor is usually integrated into the rearview mirror mount or located near the base of the windshield, on the dash. As for the wiring, check for any frayed wires, loose connectors, or green/white corrosion on the terminals. If you're not comfortable with electrical troubleshooting, it might be worth taking it to a workshop. They can properly diagnose the issue and replace the sensor or repair the wiring as needed.

Thanks for the info! I think I'll take your advice and bring it to a shop. I got a quote for around 95€ to replace the sensor and fix the wiring. Seems reasonable enough, and way less of a headache than me messing something up. Appreciate the help!