In a notice sent to VW dealers last week and obtained by Automotive News today, VW said it will begin notifying customers of the service campaign on May 28.
"As diesel engine passenger vehicles become more popular, auto manufacturers have seen an increase in the number of misfueling cases where diesel engine vehicles are mistakenly fueled with gasoline," according to the notice. "The resulting fuel system contamination can lead to costly repairs that are not covered under warranty."
The company said it will pay for authorized dealers to add a misfueling guard and fuel filler neck cap to affected 2009-12 vehicles.
Beginning with 2013 vehicles, VW redesigned its fuel fillers to accept only diesel nozzles. Gasoline nozzles are smaller than diesel nozzles. But with one of the new TDI fuel fillers, if a driver tries to insert a gasoline nozzle instead of a diesel nozzle, the fuel tank gate will remain closed.
VW has been a strong proponent of diesel-fueled vehicles in the United States. But improper fueling has become an occasional source of tension between VW and its vehicle owners, online message boards show, because fueling a TDI model with gasoline voids its warranty.
VW spokesman Tony Cervone said the problem stems from American consumers' unfamiliarity with diesel fuel.
"It hasn't been as frequent in their lifetime to remember to fill up with diesel," Cervone said in an interview.
Just 0.8 percent of 2012 light vehicles sold in the United States were diesels, up from 0.1 in 2008, according to EPA data. In some parts of Europe, about half of light vehicles sold run on diesel.
VW has blamed misfueling for a spate of failed high-pressure fuel pumps that has led to an investigation by auto safety regulators.
The National Highway Traffic Safety Administration started an investigation into several diesel-fueled VW models in February 2011 after receiving dozens of complaints about cars that stalled, often at highway speeds.
These complaints were typically linked to a failed fuel pump. VW told NHTSA investigators that 90 percent of the fuel samples from vehicles involved in the complaints had substantial amounts of gasoline in their tanks.
To date, NHTSA has received 160 complaints and field reports, many of them submitted by VW, according to the agency's official log of the investigation.
The investigation has been upgraded to an engineering analysis, which can lead to a recall, but no such step has been taken.