EGR ...Exhaust Gas Recirculation ... The egr pumps alittle exhaust gases back into the combustion chamber to "cool" the chamber ....The cooling of the chamber reduces the NOx the chamber makes .... Modern smog motors at one end are trying to cool the fuel charge and on the other end trying to get the exhaust real hot (CAT) to burn any fuel that the combustion chamber did not burn ... <img src="/forums/images/graemlins/confused.gif" alt="" />...

I know ..I know ... Sounds strange hot exhaust gases "cooling" a cylinder...

The whole Cat and EGR systems in modern cars is a scam ...Theirs better ways to redos smog but those in charge would not make the big money ...