The process VW used to reduce NOx has been superseded by the use of DEF fluid. It was called the Lean NOx process which relied on heating the catalytic converter at times by spraying the exhaust gas with raw fuel, kind of like an afterburner but it didn't help move the vehicle, only heat up the exhaust enough to address the NOx being generated. Wasteful. Diesels using DEF or Urea injection only cost the price of the DEF fluid along with the dosing system and converters. Still expensive, but they done waste fuel. Wait till Diesel Particulate Traps are mandatory. The exhaust system will cost almost as much as the engine.
