Неисправная дроссельная заслонка EGR

The throttle in the intake tract used to create the pressure difference that drives exhaust gas recirculation, as distinct from the recirculation valve itself. It is an intake throttle doing an emissions job, and the two are constantly confused because both carry "EGR" in their names while sitting in different places and failing differently.

Its purpose is counter-intuitive: it closes to make the engine breathe worse. On a diesel the intake is otherwise unthrottled, so there is little vacuum to pull exhaust gas in — this valve restricts the intake to create the differential. So a seized-open throttle produces insufficient recirculation flow with a perfectly good recirculation valve fitted.

Carbon is the mechanism, and it accumulates on the shaft and bore. The complaint is a valve whose actuator cannot reach the commanded position, or one that sticks and then jumps. Check the effort needed to move it by hand before condemning the actuator — a seized shaft with a healthy motor and a free shaft with a failed motor give the same code and different repairs.