C4 Rear Window Heating Issue

I also have a C4. I had a similar problem with my rear window defroster last winter. 'Error stored in the error memory' sounds like the car's computer has detected a fault. The windshield heating being affected too is interesting. Do you know if your battery has been tested recently? A heavily discharged or defective battery can cause all sorts of weird electrical issues in these cars. It's worth checking before you start tearing things apart looking at the heating coil itself.

Cheers for the quick reply! No, the battery hasn't been tested recently. Where would I even start checking that? And what's the deal with the heating coil? Is that likely to be the culprit if the battery is ok?

Given the symptoms, I strongly suggest having a professional test the battery's health. The heating coil is responsible for the actual defrosting. But, if the battery isn't providing enough power, the coil won't function correctly, even if the coil itself is perfectly fine. It is also connected to the car's electrical system with fuses and relays. A diagnostic in the workshop will be much more efficient than randomly replacing parts, especially with a stored error code.

Took it to the workshop, and they confirmed it was the battery. Heavily discharged, just like you thought. New battery fitted, and the rear window heating is working again. Cost me 290€ Thanks for the advice!