گرفتگی خنک‌کن EGR

The heat exchanger cooling recirculated exhaust gas, blocked internally with soot so flow is restricted. It is downstream of the valve and upstream of the intake, and it is the part most often left alone when a recirculation fault is repaired.

A blocked cooler produces an insufficient-flow code with a valve that works perfectly. So it is the second reason a replaced valve fails to fix the fault — the first being blocked passages — and both are invisible with the valve in place. A valve that moves through its full commanded travel while flow codes persist points downstream.

Coolers also fail by leaking, which is more serious: an internal crack lets coolant into the exhaust stream, showing as white smoke, unexplained coolant loss and a pressurised cooling system. Check the coolant level and look for white smoke while diagnosing a blockage, since a cooler that is both blocked and cracked is common and the leak is the finding that matters.