Резьба датчика прикипела в выпускном тракте

A sensor seized into its exhaust boss by corrosion and heat cycling, which is a repair obstacle rather than a fault in itself — but one worth naming, because it changes what the sensible repair is and it is how a small job becomes a large one.

The risk is the boss, not the sensor. Forcing a seized oxygen or temperature sensor commonly shears it, strips the thread, or twists the boss out of the pipe — and the repair escalates from a part to a welded insert or a new section of exhaust. A sheared sensor with its body left in the pipe is the worst outcome and is entirely avoidable.

Heat and patience are the method. Work on a warm-but-not-hot exhaust so the metals have expanded and separated, use penetrating fluid with time to act, and use the correct slotted socket rather than a spanner on the flats. Anti-seize on the new sensor's threads is the step people skip, and it is what stops the next person meeting the same job — though it must be kept off the sensing element itself, which the manufacturer's instructions will say.