In this process, the abbreviation "EVAP" (evaporative emissions) stands for the verification of evaporative emissions. An activated charcoal filter in the tank system already prevents petrol vapours from being released into the environment of Volkswagen models. In the past, this was tested in an airtight chamber for 24 hours. In the future, however, the period will be 48 hours – at constant limit values. The vehicles will be retrofitted with technology to meet these additional requirements.
Another major change with the second WLTP stage is the measurement of whether the emission limits are still met during vehicle operation. In future, vehicles up to five years old will be subjected to a random WLTP test. This field monitoring (ISC = InServiceConformity) is carried out on selected vehicles with a mileage of up to 100,000 kilometres. Volkswagen also uses a mobile exhaust gas measurement laboratory for on-site measurements of customer vehicles.
The first WLTP stage came into force for all new vehicles on 1 September 2018. The fact that the next stage follows just one year later – and there will be others – is due to the procedure's high complexity. The regulations, which will come into force in September 2019, also contain details about the previous procedure and thus provide legal certainty.
The Volkswagen video explains the main changes to the WLTP cycle, which will be mandatory from September 2019: https://youtu.be/lZXdQYSF1Gk