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Montana Exhaust & Muffler Laws (2026)

Info: Your vehicle needs a muffler in good working order that prevents excessive noise and smoke, and muffler cutouts and bypasses (which route exhaust around the muffler) are prohibited.

InfoVerified Jun 19, 2026

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Your vehicle needs a muffler in good working order that prevents excessive noise and smoke, and muffler cutouts and bypasses (which route exhaust around the muffler) are prohibited. Montana sets no fixed decibel limit (Mont. Code Ann. § 61-9-403).

Official source: mca.legmt.gov →

General legal information, not legal advice — verify important decisions with a licensed attorney.

Exhaust & Muffler in states bordering Montana

The same rule in each neighboring state LawLert has verified, from that state’s own official source.

IdahoInfo
Your vehicle needs a muffler in good order, and cutouts and bypasses (which route exhaust around the muffler) are banned, along with changes that make the exhaust louder — in Idaho, "excessive noise" means more than 92 decibels measured at 20 feet (Idaho Code §§ 49-937, 49-106).
Verified Jun 19, 2026 · Source: legislature.idaho.gov · Full Idaho rule →
North DakotaInfo
Your vehicle needs a muffler in good working order, and a cutout or bypass (which routes exhaust around the muffler) is prohibited while excessive or unusual noise is barred. North Dakota sets no fixed decibel limit (N.D. Cent. Code § 39-21-37).
Verified Jun 19, 2026 · Source: ndlegis.gov · Full North Dakota rule →
South DakotaInfo
Your vehicle needs an exhaust system and muffler in good working order, the exhaust has to discharge to the rear or the side, and muffler cut-outs (which route exhaust around the muffler) are prohibited. South Dakota sets no fixed decibel limit (SDCL § 32-15-17).
Verified Jun 19, 2026 · Source: sdlegislature.gov · Full South Dakota rule →
WyomingInfo
Your vehicle needs a muffler or other effective noise-suppressing system in good working order, and a cut-out, bypass or similar device (which routes exhaust around the muffler) is prohibited. Wyoming sets no fixed decibel limit (Wyo. Stat. § 31-5-953).
Verified Jul 22, 2026 · Source: wyoleg.gov · Full Wyoming rule →

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