After the breakup of the USSR, a licensed version of the Volkswagen Polo engine replaced the Trabant's two-stroke engine, the result of a trade agreement between East and West Germany. East Germanys needed a special permit to drive their older Trabant 2-strokes into the country as they were massive polluters. The model was discontinued in 1991. The Zwickau factory in Mosel (where the Trabant was manufactured) was sold to Volkswagen AG; the rest of the company became HQM Sachsenring GmbH. Volkswagen redeveloped the Zwickau factory into a centre for engine production; it also produces some Volkswagen Golfs and Passats.