C6 Diesel Cold Start PTC Heater

Sounds familiar. I had a similar issue with my old Peugeot diesel. Cold starts were a nightmare, and the fuel consumption was ridiculous. Error codes pointed towards heating issues too. Did you check the voltage reaching the PTC heater? If it's not getting enough juice, it might struggle to warm things up properly. It could also be a faulty temperature sensor giving the heater the wrong readings. I am not sure it is the heater itself but who knows.

Thanks! Voltage to the PTC heater is a good idea. I'll check with a multimeter. Where is the PTC heater located on the C6? What should the voltage be? Is there a specific temperature sensor for the PTC heater, or the main engine coolant temperature sensor?

I don't know the C6 specifically, but usually the PTC heater is near the ventilation system or the main heater core. I'm not sure about the exact voltage values for your car, but you should find the information in the service manual or online. If the voltage looks good, the heater itself is most likely defective. Honestly, unless you are very confident with electrics, it might be worth a trip to a workshop. It'll save you the headache and probably time.

I appreciate the advice! I'll poke around with the multimeter, but electrics aren't my strongest suit, and I don't want to risk damaging anything. I'll book it in at the local garage. They quoted me around 350€ for replacing the PTC heater, which seems reasonable. Thanks again for pointing me in the right direction!