Exhaust Gas Recirculation is recirculation of combustion gases from the exhaust manifold so they are burned by the engine rather than emitted. The trouble is EGR valves get clogged with hydrocarbon tars. They can sometimes be cleaned up with solvents after removing them.

But a dealer regards this as too much trouble and simply replaces them. Renault’s answer in its new 1.6 DCI 130 engine is an EGR system that takes the gases from after the diesel particulate filter, cools them, then recirculates them through the intercooler making sure they are recombusted at the right temperature.