SCR
Selective Catalytic Reduction
An SCR is a special catalyst installed into the exhaust systems of modern diesel vehicles.
The SCR injects AdBlue into the exhaust gases under pressure. The SCR typically has a head made from Zeolite (Ceramic).
SCR's are very susceptible to damage from foreign matter. They can also be rendered ineffective by AdBlue where its structure has changed due to the de-ionised water stripping ions from incorrectly.

