Peugeot 4008 Overheating

Overheating and a check engine light certainly point to cooling issues. A defective speed sensor could affect the fan's operation, but it's a bit indirect. Have you checked the fan motor itself, and are the fan blades obstructed?

Good point! Motor seems dead as a doornail. Blades are clear. But still wondering, could that sensor throw everything off even if the motor is gone?

If the fan motor is confirmed non-functional, the speed sensor is likely a secondary issue, or a consequence. It's best to address the primary fault first. Given your expertise, I would recommend a workshop visit.

Cheers! Turns out it was the motor, just as you suspected. New fan motor and sensor replacement later, I'm 250€ lighter, but she's running cool. Thanks for the sanity check!