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Vehicles required to meet the emission standards of this part must meet the following additional requirements, except as noted elsewhere in this part:
(a) Adjustable parameters. Vehicles that have adjustable parameters must meet all the requirements of this part for any adjustment in the practically adjustable range. We may require that you set adjustable parameters to any specification within the practically adjustable range during any testing. See 40 CFR 1068.50 for general provisions related to adjustable parameters. You must ensure safe vehicle operation throughout the practically adjustable range of each adjustable parameter, including consideration of production tolerances. Note that adjustable roof fairings are deemed not to be adjustable parameters.
(b) Prohibited controls. You may not design your vehicles with emission control devices, systems, or elements of design that cause or contribute to an unreasonable risk to public health, welfare, or safety while operating. For example, this would apply if the vehicle emits a noxious or toxic substance it would otherwise not emit that contributes to such an unreasonable risk.
(c) [Reserved]
(d) Defeat devices. 40 CFR 1068.101 prohibits the use of defeat devices.
[86 FR 34459, Jun. 29, 2021; 88 FR 4637, Jan. 24, 2023; 89 FR 29771, Apr. 22, 2024; 91 FR 7786, Feb. 18, 2026]