Auris rear window heating issue

A weak battery can definitely mess with the electrical systems. Have you checked the battery's voltage? What voltage are you getting when the car is off and when it's running?

I haven't checked the voltage yet, but I can. Where should I measure for an accurate reading? What values should I look for when the car is off and running to confirm the battery is the problem?

Measure directly at the battery terminals. With the car off, you should see around 12.6V for a healthy battery. When running, it should be around 13.7V to 14.7V, indicating the alternator is charging. If it's significantly lower, especially when running, the battery or charging system is likely the issue. Given the error code, both heaters acting up, and your mileage at 151240 km, I'd suggest getting it checked at a workshop before replacing parts.

Voltage was indeed low. Replacing the battery fixed the rear window heater. Total cost was 290€, including the new battery and installation. Thanks for the help!