EGR Cooler

It is common on diesel engines and some petrol engines. It uses engine coolant. A bypass valve lets hot gas skip the cooler when the engine is cold. Diagnosis often includes a cooling system pressure test and checking for coolant in the intake.

Exhaust gas passes through tubes surrounded by coolant and gives off heat.

A leaking cooler can cause coolant loss, white smoke and in severe cases engine damage. Soot can block it, raising EGR flow codes.