Modus Cold Start PTC Heater

Sounds like a classic PTC heater failure. The diesel Modus uses it to help warm the cabin and engine faster. If it's gone, you'll get poor cold running and the increased fuel burn you describe. Have you checked the heater element itself for continuity?

Thanks. I haven't tested the heater element. Could you explain how, or point me to a resource? I'm okay with basic electrical testing, but want to be sure I do it right.

Given your description, I'd advise against DIY testing unless you're very confident with automotive electrics. The Modus's heater circuit can be tricky. To avoid damage or injury, visit a workshop with Renault experience. They can diagnose it and replace the heater. The cost is around 350€, including parts and labor.

Thanks for the advice. I appreciate the caution about the electrics. I'll take it to a local workshop for diagnosis and repair. Knowing the likely cause and cost helps.