I found a bit of an answer. According to this EPA document, it detected a test by sensing the position of the steering wheel, vehicle speed, duration of engine

I found a bit of an answer. According to this EPA document, it detected a test by sensing the position of the steering wheel, vehicle speed, duration of engine operation and barometric pressure. http://www3.epa.gov/otaq/cert/documents/vw-nov-caa-09-18-15.pdf http://www3.epa.gov/otaq/cert/documents/vw-nov-caa-09-18-15....