It was phased in on the bigger, heavier cars first. The current US-model Passat has used SCR since it was introduced, as has the Touareg with the and every othe

It was phased in on the bigger, heavier cars first. The current US-model Passat has used SCR since it was introduced, as has the Touareg with the and every other VW/Audi with the 3.0L V6 TDI. VW didn't put it in the Golf or Jetta until 2015 because it takes up room, adds cost and complexity. By 2015 emissions standards got tight enough that they had no choice. Prior to that the Golf and Jetta used a NOx catalyst that requires a periodic burn-off achieved by sending a pulse of unburned fuel down the exhaust. Same deal as the particulate trap--that stuff needs to be burned off every so often, too.