تنگی مسیر خنک‌کاری انژکتور اوره

The coolant passage cooling the reductant injector, restricted. The injector sits in the exhaust and would otherwise cook, so it is plumbed into the engine's coolant — and its passages are fine enough to block with sediment.

Without cooling the injector overheats, the reductant in its tip dries and crystallises, and the spray is blocked by the very deposit the cooling exists to prevent. So a coolant restriction presents later as a dosing fault, and replacing the injector without clearing the passage crystallises the new one too. Check coolant flows through the injector's circuit rather than assuming, and treat sediment there as a statement about the whole cooling system's condition.