Aftermarket Exhaust in Illinois
Replacing the exhaust system is legal in Illinois, but a muffler in good working order is required and cutouts or bypasses are prohibited. There is no statutory 'no louder than stock' rule — the standard is that the exhaust must not produce excessive or unusual noise.
Verified against primary sources · August 2026
What the law says
Replacing the exhaust system is legal in Illinois, but a muffler in good working order is required and cutouts or bypasses are prohibited. There is no statutory 'no louder than stock' rule — the standard is that the exhaust must not produce excessive or unusual noise. Removing the catalytic converter is prohibited by federal law (Clean Air Act § 203) regardless of state rules. Chicago-area and Metro-East counties require OBD emissions testing.
Specific Limits
- Cutouts
- prohibited
- Muffler required
- Yes
- Louder than stock
- not addressed; excessive noise standard applies
- Catalytic converter
- removal prohibited by federal law
Exceptions & Exemptions
Must have working muffler that prevents excessive noise. Catalytic converters required on vehicles originally equipped with them. Exhaust cutouts, bypasses, or straight pipes that allow exhaust to exit before the muffler are prohibited.
Frequently Asked Questions
Are aftermarket exhaust legal in Illinois?
What are the exact aftermarket exhaust limits in Illinois?
Are there exceptions for aftermarket exhaust in Illinois?
Street-legal aftermarket exhaust picks
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