RCZ Mirror Heating Defective

A defective heater element is possible, although less common than wiring issues. Have you checked the relevant fuses and relays associated with the mirror heating circuit? Also, inspect the connector at the mirror itself for corrosion or loose pins. The temperature control module might be faulty, but that's less likely if both mirrors failed simultaneously.

Fuses and relays are fine. Where exactly is the temperature control module located?

The temperature control module's location can vary, but it's often integrated within the door control module or the body control module. Given the diagnostic information, and the process of elimination, I suggest that you bring the car to a workshop.

Thanks. As predicted, cable or plug connection defective. Repair cost: 95€