انسداد ممر إعادة تدوير العادم بالكربون

A single recirculation passage blocked with carbon, restricting flow while the valve itself works correctly. The module measures the result rather than the valve's position, so a valve that opens fully into a blocked passage produces an insufficient-flow code with nothing wrong with the valve.

This is the reason a replaced valve so often fails to fix the fault. The valve is the accessible part and gets changed; the passages are cast into the manifold or the head and are left exactly as they were. A new valve and an unchanged code is the signature, and it is one of the most common wasted repairs on a diesel.

Inspect with the valve removed rather than inferring. The restriction is often at the far end of the passage where it opens into the intake, so a bore that looks clear at the valve face can be almost closed further in. Short journeys and cool exhaust accelerate it, since deposits that never get hot enough to bake off simply accumulate — which is worth telling an owner whose usage will reproduce it.