Hi, I had a similar problem with my 2008 Citroen C3, I would say I have some experience with cars. My garage found out that the cold shut-off valve was faulty, which caused the problem. The good part is that it didn't cost me anything because it was under warranty. Can you provide more details on the problems and symptoms? Maybe then I can help even better.

(Translated from German)

Hey, thanks for your answer! So the problem usually occurs when I've been driving long distances. Then the ventilation also starts to go crazy and it smells funny. My DS3 now has 119239 KM on the clock and the last workshop visit was at the 100000 KM service. Hope this helps you!

(Translated from German)

That really doesn't sound good and the smell is a clear sign that something is wrong. It was similar with my C3 at the time. It was actually the air conditioning system that had a loose connection. In my case, however, the fault was not in the message, but in the power supply. Have you had any problems with the battery recently? Or any work on the electrics? It could also be that your DS3 has a coolant leak and that explains the smell. Or even worse, the heating coil could be broken. In any case, I would advise you to take your car to the garage. Maybe it's just a minor issue, but it's better to have it checked. Stay on the ball and let me know what comes of it.

(Translated from German)

Jo, many thanks for the tips! There have indeed been problems with the battery recently and I only recently had it replaced. I also suspected the coolant leak, so we'll see what it really is. I'll make an appointment at the garage tomorrow and let you know what I find out. Thanks again, your information was really helpful!

(Translated from German)