Capteur de régime d'arbre intermédiaire défectueux

The sensor reading the speed of a shaft partway through the gearbox, between input and output. Its purpose is to let the module see inside the transmission — with input and output speeds alone it can calculate an overall ratio, but not which element slipped. The intermediate reading tells it which half of the gear train is misbehaving.

So a fault here removes precision rather than function. The transmission usually still shifts, but the module loses its ability to attribute a ratio error and will often adopt a conservative strategy, so the complaint is harsh or lazy shifting alongside a set of ratio codes. Those ratio codes are the ones that mislead, since they read as mechanical failure while the gearbox is sound.

These sensors are internal on most designs, which changes the economics: the pan or the valve body has to come off, so establishing the fault properly before starting is worth the effort. Compare all three speed readings in live data — one that drops out, reads zero while the vehicle moves, or produces an impossible ratio against its neighbours is the sensor. Its wiring passes through a case connector, which is a common failure point and far cheaper to fix than the sensor behind it.