Bad PTC Heater Causing Cold Starts and Fuel Spike?

Had the exact same heating system issue on my 2012 Chevy Silverado last winter. The electrical fault in the PTC heater was causing similar cold start problems, rough idle and increased fuel consumption. The temperature control system wasn't regulating properly because the heating element was stuck in a constant "on" state. Our shop diagnosed it using advanced diagnostics and found the PTC heater assembly was failing intermittently. This is actually a pretty serious problem since it can damage other electrical components if left unfixed. The repair required replacing the entire PTC heater unit and recalibrating the temperature control module. Definitely not a DIY job due to the electrical system complexity. Though it sounds daunting, it's a known issue with a straightforward fix for an experienced tech. Before going to a shop, check if your coolant levels are good and inspect for any visible damage to heating system wiring. But given the stored error code and symptoms, it's likely the PTC heater assembly needs replacement.

Thanks for the detailed reply! Your Silverado's symptoms sound identical to what I'm experiencing. Been dealing with this heat not working properly and the rough cold starts are getting really annoying. The blower motor works but it's just pushing cold air most of the time. Mind sharing what the repair ended up costing you? Also curious if you've had any other issues pop up since getting it fixed? Want to make sure I budget properly and know what to expect when I take it in.

Thanks for asking about the costs. The fix worked out great and fully solved the HVAC system issues. The repair bill came to 350€ for replacing the faulty electric auxiliary heater and doing all the necessary electrical fault diagnostics. Since getting it fixed, the heating system has been working perfectly, no more cold starts or temperature control problems. My fuel consumption is back to normal too. The blower now pushes properly heated air, and the PTC heater kicks in exactly when it should. Haven't had a single issue with it for the past months. The mechanic explained that these electrical heating elements can fail over time, but once properly replaced, they typically last for many years. It was definitely worth getting it done professionally rather than trying any DIY fixes, given all the complex electronics involved. The peace of mind knowing the heating system is working correctly again made the cost worthwhile. Plus, preventing potential damage to other electrical components by fixing it promptly probably saved money in the long run.

Just wanted to update everyone on how this turned out. Finally got my Avalanche fixed last week after finding a reputable shop that specializes in HVAC system repairs. The diagnosis was spot-on, it was definitely the PTC heater causing all the trouble. The repair cost me around 400 Euro total, which included replacing the heating element and some diagnostic work. The mechanic showed me the old PTC heater and it was pretty obvious it was shot. They also cleaned out the blower motor while they were in there since it had collected some debris. Started up the truck this morning and what a difference! No more rough idle, the cold air problem is completely fixed, and the engine runs smooth right from startup. Fuel gauge isn't dropping like a rock anymore either. The HVAC system is working exactly like it should, warm air comes through strong and fast. Really glad I got this sorted before winter. The shop did great work and even gave me a 1-year warranty on the parts. Would definitely recommend getting this fixed sooner rather than later if anyone else runs into similar symptoms.