Up until the end of 1995 a dual IM system had been in effect in Mexico City combining both centralized (test only) facilities and decentralized private garages (combined test and repair).

Over time, it became increasingly clear that the private garage system was not working. As one measure, for example, the failure rate in the private garages averaged about 9 percent whereas in the centralized lanes, the failure rate was about 16 percent.

Stations conducting improper or fraudulent inspections were taken to court on several occasions with the courts usually agreeing to shut them down. By the end of 1995, as part of the development of the "Programma para Mejotrar la Calidad del Aire en el Valle de Mexico, 1995-2000" (the New Program), and in recognition of the critical role that IM had and would play in the Mexico City strategy, the Federal District (DDF) decided to close all the private garage inspection stations and to switch to a completely centralized system. This politically difficult decision reflected a conclusion that it would be virtually impossible to police the private garage system on a case-by-case basis.