The problem wasn't just that it was an inconvenience. Under the EPA rules of the time, urea refills were considered critical emission-related maintenance. Initi

The problem wasn't just that it was an inconvenience. Under the EPA rules of the time, urea refills were considered critical emission-related maintenance. Initially, this meant that they had to last 100,000-150,000 miles unless the EPA gave a waiver allowing more frequent servicing intervals.[1] This wasn't physically feasible. A couple of years into Dieselgate, they decided they'd allow DEF refills at the oil change interval, which still required much larger tanks than the European models (typically replacing the spare tyre) or cheating.[2] It wasn't until mid-2014 that they decided users could be allowed to refill their own urea tanks and lowered the minimum DEF refill interval for cars to a slightly more reasonable 4,000 miles.[3] [1] https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=16677&flag=1 https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=16677&... [2] https://www.govinfo.gov/content/pkg/FR-2009-11-09/pdf/E9-26924.pdf https://www.govinfo.gov/content/pkg/FR-2009-11-09/pdf/E9-269... [3] https://www.govinfo.gov/content/pkg/FR-2014-08-08/pdf/2014-18738.pdf https://www.govinfo.gov/content/pkg/FR-2014-08-08/pdf/2014-1...