Lexus RC Rear Window Heater Issue

A fault code and both heaters acting up? Sounds like an electrical issue. When you say 'error memory', do you have a code reader? Knowing the code would help. Both heating elements being affected makes me suspect a power supply issue. By 'less effective,' do you mean it takes longer to clear, or doesn't clear fully?

I don't have a code reader. By 'less effective' I mean it takes much longer for the windshield to clear.

A 'power supply issue' could mean a few things, but given the symptoms and the car's age, I'd bet on a weak auxiliary (12V) battery. Hybrids rely heavily on that 12V to boot up the system and run accessories before the high-voltage system kicks in. A discharged or defective battery could easily cause insufficient power to the heating elements, throwing codes and reducing performance. It's probably not providing sufficient current. Have the battery tested at a workshop. They can check its health and charging capacity. It's the most likely cause.

Thanks! I took it to the workshop and you were spot on – it was the auxiliary battery. They replaced it and the rear window heater is working again, and the windshield is back to normal too. Cost me 290€ including the new battery and labor. Appreciate the help!