Clogged EGR valve: symptoms, cleaning, cost and affected cars

The EGR valve sends part of the exhaust gas back into the intake to reduce nitrogen oxides (NOx). From repeated low-rev driving or short trips, it clogs up: engine warning light, misfires, loss of power. About one diesel in four suffers a clogged EGR valve before 100,000 km according to Fiches-auto (Fiches-auto), and diesels designed before 2015 are the most affected (Fiches-auto).

What is the EGR valve for?

By sending already-burnt gas back into the cylinders, the EGR valve cools combustion and limits NOx production. The flow is metered by a moving flap controlled by the engine computer (Fiches-auto). The recirculated gas is full of soot: that is what eventually jams the flap.

Symptoms of a clogged EGR valve

• a marked loss of power, often with heavy smoke;
• engine or "pollution" warning light on;
• limp mode, with the computer limiting the engine;
• misfires or flat spots under acceleration (Fiches-auto; CarVerif, Audi A6 3.0 TDI).

Be careful: an "injection" warning can actually relate to the EGR valve, and injectors are sometimes replaced wrongly when cleaning the valve would have been enough (Fiches-auto). A faulty differential pressure sensor, wiring or a corroded connector can also mimic a valve fault (Fiches-auto). Ask for a full diagnosis before spending anything.

Cleaning or replacement: how much does it cost?

Replacement is not always needed: manual cleaning or decarbonising is often enough (Fiches-auto). One Fiches-auto page prices a new valve at €200 to €350, another at €300 to €800 (Fiches-auto; Fiches-auto). The EGR cooler fitted to some diesels costs more: €600 reported on an Alfa Romeo Giulietta at 100,000 km (Fiches-auto).

Disconnecting or blanking the EGR valve is illegal under emissions rules (Fiches-auto).

When does it clog?

Mostly depending on use: short trips and low revs speed it up. Reports often place the failure beyond 100,000 km, for example between 100,000 and 140,000 km on the Audi A6 3.0 TDI (CarVerif) or after 100,000 km on the Alfa Romeo 159 1.9 JTDm (CarVerif).

Before buying a used diesel

A diesel that has mostly been driven in town is the most exposed; an engine warning light, limp mode or an AdBlue message justify walking away until the cause is fixed (CarVerif, Audi Q3 II). Ask for EGR-related invoices and have the fault codes read. See also our guide to diesel or petrol on a used car.