Lexus NX parking heater issue

Given the symptoms and error, a defective glow plug is a strong possibility. Have you checked the auxiliary heater's operational parameters, specifically the glow plug resistance, using an OBD-II scanner? Also, what's the ambient temperature when you're attempting to activate the parking heater?

Glow plug resistance? I haven't checked that specifically. Where exactly do I find that reading on the OBD-II? And does ambient temp really matter that much? It's been around 5°C lately when I've tried.

Yes, ambient temperature is a factor, though 5°C should generally be within the operating range. Regarding the OBD-II reading, you'll typically find it under 'Auxiliary Heater' or 'Parking Heater' diagnostics, then 'Glow Plug Resistance.' However, given your equipment and experience, I would advise taking it to a qualified workshop. Ignoring the issue can lead to damage of other components.

Thanks, that confirms my fears! Booked it in with a local shop. They ran the diagnostics and yup, glow plug was toast. 440€ later, all fixed. Appreciate the help!