Capteur de température de refroidissement de l'onduleur défectueux

The sensor measuring the temperature of the coolant serving the power electronics has failed or drifted.

What makes this worth more than an ordinary sensor fault is how much rests on the number. The reading governs two limits at once: how much torque the car will deliver, and how fast it will let itself charge. Both are set by what the inverter, the on-board charger and the DC/DC converter can safely tolerate, and all three are judged from this circuit.

So a sensor reading falsely high makes a perfectly healthy car derate and charge slowly, and there is nothing else visibly wrong to explain it. That is the case that gets chased through expensive components. Reading falsely low is rarer and worse, because the protection that should intervene never does.

The most useful clue is that it should not be alone. Power electronics on a shared coolant loop cannot be at wildly different temperatures, so comparing this reading against the other sensors in the same circuit — the inverter's own, the converter's — settles it quickly. One sensor disagreeing with its neighbours is the sensor. All of them rising together is the cooling.

And the cheap thing first: the electronics coolant circuit is a separate reservoir from the engine's on most vehicles, easy to overlook at service, and awkward to bleed — so low coolant and trapped air both produce readings that look like a failed sensor.