Xterra Auxiliary Heater Problem

I had a similar predicament with my previous vehicle, a 2012 Volvo XC70. The symptoms you describe align with a potential malfunction of the glow plug within the auxiliary heater system. Have you examined the electrical connections to the heater core and the temperature sensor? Is there any evidence of a coolant leak, as this can sometimes affect the performance of the auxiliary heating system?

Coolant leak I've checked and seems fine. Temperature sensor seems okay, at least the main one. But the glow plug... where exactly is that located within the heating system? Is it easy to get to? Don't want to start tearing things apart blindly.

Accessing the glow plug typically necessitates partial disassembly of the auxiliary heating unit. Given the presence of an error code and the potential complexity of accessing the component, I would recommend consulting with a qualified automotive technician. It is likely the glow plug is defective and requires replacement.

Thanks for the advice! Took it to the shop like you suggested. Turns out it WAS the glow plug in the auxiliary heater, just like you called it. Cost me about 440€ to get it sorted, but at least it's fixed. Really appreciate the help!