EGR
Exhaust Gas Recirculation feeds a measured dose of exhaust gas back into the engine’s intake to lower combustion temperatures and cut nitrogen oxide (NOx) emissions. It’s fitted to most modern petrol and diesel cars — and the EGR valve is a notorious failure point: carbon build-up causes rough running, warning lights and failed MOT emissions tests. Regular longer runs and quality fuel help keep it clean.
Example
A clogged EGR valve typically shows as hesitant acceleration and an engine management light around 60,000–100,000 miles.