2013 and 2014 Mercedes-Benz C-Class models are the latest subject of a fuel economy adjustment by the EPA, as the agency has revised city fuel economy numbers slightly downward after finding an error in Mercedes’ calculations during audit testing.
The affected 2013 and 2014 Mercedes-Benz C300 4Matic models will have new EPA ratings of 19/28/22 mpg city/highway combined, 1 mpg lower all around compared with the previous ratings. Flex-fuel capable versions of the C300 4Matic lose 1 mpg city, for new ratings of 19/27/22 mpg.
Because automakers internally test for fuel economy and then submit numbers to the EPA, audit testing exists to periodically check in on these internal results to make sure they correspond with the EPA’s official testing methods. In this case, the EPA found that Mercedes-Benz’s error involved the way it calculated the impact of road-load resistance numbers such as aerodynamic drag and tire rolling resistance. This is the same issue Ford faced in its recent fuel economy revisions. The EPA says it also tested other Mercedes models and did not find any other inaccuracies with fuel economy ratings.
Mercedes-Benz will re-label all 2013 and 2014 C300 4Matic models as a result of this finding, although the company has not yet announced any sort of reimbursement plan for owners of these cars.