Cat Converters , ERG and Add Blue are all stopgap measures cobbled together on the run to meet emissions standards to minimise NOX & Carbon Monoxide gases.
Unfortunately there are conflicting principles at play here:
The objective is to extract max useable energy out of the fuel burnt and that entails getting as much oxygen and controlled fuel into the cylinder as efficiently as possible and then fully burn the fuel.
This increases combustion chamber temperatures which n turn generate more NOX gases and thisis where the fiddling with the fine tuning of the exhaust (preferably only CO2 & HO2) begins
The result is for some of the rev band that metered exhause gases are re-introduced into the cylinder thereby reducing chamber temps and NOX emissions and of course making the engine less fuel efficient and shortening the engine's life via the free carbon micro granules ; hence the syl wal polishing (wear), loss of compression and oil burning.
Toyota went through a stormy patch on the early-mid Zeroes with this (just have a look at the Car Nut on Youtube) and the shorter term part fix seemed to be more frequent oil changes -
