تراكم الكربون في نظام إعادة تدوير العادم

Soot and oil mist combining into a hard, tar-like deposit through the recirculation path. It is not dirt — it is the system doing its job. EGR deliberately routes exhaust gas into the intake, and on a diesel that gas carries particulate; mixed with oil vapour from the crankcase breather it bakes onto every surface it touches.

Which makes this the single most common mechanical cause across the whole EGR family, and the reason so many of its codes are really one fault. It binds the valve so it neither opens nor closes fully; it narrows the ports until the valve can be wide open and little passes; it shifts the valve's rest position until the module's adaptation runs out; and it coats the temperature sensors so they read low.

Cleaning is a genuine repair here rather than a delaying tactic, provided the actuator is sound and the spindle is not worn — which matters, because these valves are expensive and the passages have to come apart either way.

Driving pattern is the real cause underneath the deposits. Short, cold journeys never get the system hot enough to burn deposits off, so they accumulate steadily. Occasional sustained runs genuinely slow it down, and a valve cleaned without changing that simply coats again.