Q: How to Replace an EGR Valve?A: The Exhaust Gas Recirculation (EGR) system reduces nitrogen oxides (NOx) produced by your vehicle's engine by reintroducing exhaust gases into the intake manifold, dropping combustion chamber temperatures. To replace the EGR valve, disconnect the negative battery terminal and the EGR valve's electrical connector. Clean any exhaust deposits and if the EGR passage is clogged, clean it with a wire wheel.