40 CFR 91.111 - Requirement of certification
(b) For purposes of this section, defeat device means any device, system, or element of design which senses operation outside normal emission test conditions and reduces emission control effectiveness.
(1) Defeat device includes any auxiliary emission control device (AECD) that reduces the effectiveness of the emission control system under conditions which may reasonably be expected to be encountered in normal operation and use, unless such conditions are included in the test procedure.
Title 40 published on 2013-07-01
no entries appear in the Federal Register after this date.