Capteur de température de refroidissement de l'échangeur défectueux

The temperature sensor in the low-temperature coolant circuit that serves a liquid-cooled charge air cooler. That circuit is a second, separate cooling system — its own pump, its own radiator, its own reservoir, running deliberately cooler than the engine's — and this sensor is how the module knows it is working.

Its faults are mostly diagnosed by inference, which is what makes this sensor worth suspecting. The module often judges cooler efficiency and pump performance by comparing expected temperatures against measured ones, so a drifting sensor sets efficiency and performance codes against hardware that is entirely healthy. Verify it before anything is replaced on the strength of what it reported.

The cheap check is a cold soak: after the vehicle has stood overnight, this sensor should read close to ambient and close to every other temperature sensor on the vehicle. One that does not has declared itself without a road test. Note that the reservoir it serves is not the engine's expansion tank and is routinely missed at service, so a low level in that circuit produces similar symptoms with a sound sensor.