Auxiliary Heater problem

That's a weird one. Auxiliary heater issues can be tricky. Have you noticed any coolant leaks recently? Sometimes a small leak can cause pressure issues that prevent the heater from firing up. Also, how's your heat control inside the car? Does the regular heating system seem to be working okay, or is it acting up too?

Thanks for the quick reply! I haven't seen any obvious coolant leaks, but I'll definitely give it a closer look. The regular heating system seems to be working fine – good heat output and no strange noises. Could it still be related, even if the main heater is working?

Hmm, if the main heater is working, that does make it less likely to be a general climate control issue. However, since you're getting an error code specifically for the auxiliary heater, and it won't activate, it's pointing towards a problem within the auxiliary heater system itself. A common culprit in these older systems is a defective glow plug. It might be worth getting it checked out by a workshop, as diagnosing these systems can sometimes require specialized tools.

Thanks, I appreciate the advice! I took it to a local shop, and you were right – turns out it was a defective glow plug in the auxiliary heater. They replaced it, and everything's working perfectly now. Total repair cost was 440€ Thanks again for pointing me in the right direction!