Subaru Auxiliary Heater Failure, Quick Fix Guide

I faced a similar issue with my 2005 Subaru Legacy last winter. The car heater malfunction started with the error light, and the heating system stopped responding entirely. The ventilation system would blow only cold air regardless of temperature settings. Initial diagnosis revealed a faulty heat control module and damaged wiring to the auxiliary heater unit. The repair involved: Complete diagnostic scan, Replacement of the auxiliary heater control unit, Repair of corroded wiring harness, System reset and testing This was definitely a serious issue that required professional attention. Driving without a properly functioning heater core can lead to additional problems, including windshield fogging and reduced defrosting capability. Based on the symptoms you describe, it sounds very similar to what I experienced. These auxiliary heater failures often stem from electrical issues rather than mechanical problems. Would strongly recommend having it checked by a qualified mechanic since the issue typically gets worse if left unaddressed. The full repair took about 6 hours at the shop, and the heater has worked flawlessly since then. Just ensure they perform a complete system diagnostic before starting any repairs.

Thanks for sharing your experience with the auxiliary heater issue. After fixing my heat control module, I also noticed the temperature sensor had to be recalibrated. My climate control system has been working perfectly for the past 8 months with no errors. Would you mind sharing what the total repair cost was in your case? Also curious if you had any other heating-related problems pop up since getting it fixed. The heater core in these models can sometimes cause issues down the line.

After taking it to the mechanic last year, the auxiliary heater problem was completely resolved. The main issue turned out to be a defective glow plug which was causing the temperature sensor to send incorrect readings to the heat control module. The total repair came to 440€, including parts and labor. The heating system has performed flawlessly since the fix. The blower motor delivers consistent airflow and the temperature control works exactly as it should. No additional heating-related issues have surfaced in the past year. The mechanic mentioned that once the glow plug is replaced and the system is properly calibrated, these heating components typically remain reliable for many years. The heater core in my Subaru has stayed in good condition, likely because the issue was addressed before it could cause any downstream damage. Getting that initial diagnosis and repair done properly really made the difference. The auxiliary heater now activates immediately when needed and maintains steady temperature output.

Thanks everyone for the helpful feedback! I wanted to share how my repair experience turned out. Got my car checked at a local shop specializing in climate control systems. The mechanic found that my auxiliary heater failed due to a burnt-out relay and damaged temperature sensor. The total repair came to 380€, which included parts, labor and a full system diagnostic. The blower motor was tested and found to be working fine, but they cleaned it while doing the other repairs. They also pressure-tested the heating system to check for any coolant leaks since that can sometimes happen with these units. Been about 2 months since the fix and everything works perfectly now. The auxiliary heater kicks in right away and maintains consistent temperature. No more error lights or cold air issues. Really glad I got it taken care of before winter sets in. If anyone else runs into similar heating problems, definitely worth getting it checked out early. The repair was much simpler than I expected and saved me from potentially bigger issues down the road.