BRUSSELS — European legislators got a jolt this month in their long-running effort to update auto-emissions standards when a German member of the European Parliament suddenly proposed exempting a whole class of vehicles.

“This was a huge loophole, and everyone was asking: Where does this idea come from?” recalled Bas Eickhout, a member of the Dutch Green party who sits on the committee on the Environment, Public Health and Food Safety.

It did not take long to discover the origin of the contentious proposal: Volkswagen Group. What had seemed a proposal by a legislator was in reality the work of the German carmaker.

This was just one particularly brazen example of how European automobile manufacturers have for years sought to thwart or water down regulation of their industry. And it helped explain one of the biggest mysteries left by the announcement this month that Volkswagen had installed software in 11 million diesel vehicles to ensure that they provided false information about emissions: Why had Europe, which has far more diesel cars than the United States, failed to uncover and halt this ruse?