This was a longstanding practice to make diesel engines more efficient while passing the official emissions test. There was a similar enforcement against Caterp

This was a longstanding practice to make diesel engines more efficient while passing the official emissions test. There was a similar enforcement against Caterpillar and other truck makers in 1998: http://www2.epa.gov/enforcement/caterpillar-inc-diesel-engines-settlement http://www2.epa.gov/enforcement/caterpillar-inc-diesel-engin... And against Ford in 1998: http://www2.epa.gov/sites/production/files/2014-06/documents/defeat.pdf http://www2.epa.gov/sites/production/files/2014-06/documents... along with a clear ruling that defeat devices were illegal.