Peugeot 206 Temperature Gauge Issue

I had similar grief with my 206. Same symptoms, long warm-up times and all that. Have you checked the grille itself for obstructions? Leaves, plastic bags, roadkill... you'd be surprised what gets stuck in there. If it's clear, start looking at fuses and sensors. Which temperature is incorrect: engine coolant temperature or ambient temperature? And does it read too low or too high?

I'll double-check for blockages, though it looked clear at a glance. The engine coolant temperature is playing up, reading too low most of the time. Which fuse should I be checking first?

If the grille's clear and the coolant temp is consistently low, it's unlikely to be just a fuse. I'd get it scanned at a workshop. Could be a faulty coolant temperature sensor, or even a thermostat issue. Better to get it diagnosed properly before throwing parts at it.

Turns out you were spot on. Took it to the garage, and after a bit of poking around, they found a defective fuse related to the fan control module, which was causing the restricted airflow issue indirectly. New fuse and diagnostic cost me 52€ and she's running sweet again.