sentences:  This, in the manufacturers' view, made it virtually impossible to ensure total compliance with the NTE—since there is no real or practical way to test an engine under all conceivable conditions—and so made the NTE both unlawful (the CAA authorizes EPA to adopt engine standards AND accompanying test procedures) and technically infeasible.On June 3, 2003, the parties finalized a settlement of their disputes pertaining to the NTE standards.The parties agreed upon a detailed outline for a future regulation that would require a manufacturer-run heavy-duty in-use NTE testing ("HDIUT") program for diesel-fueled engines and vehicles.