Vehicle Mod Laws in California

Replacing the exhaust system is legal in California, 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.

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Passenger-car exhaust may not exceed 95 dBA under the current SAE test standard; a working muffler is required and cutouts are prohibited.

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Smoked or tinted film on headlights and taillights is illegal in California. Headlights must emit white light and taillights must show red at the required visibility distance, and tint that dims or discolors them violates those requirements.

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License plate frames are legal in California as long as nothing required stays hidden. Frames are fine if the plate, registration tabs, and state name remain legible — including to electronic readers. Covers are banned, with a narrow exception for a security cover strictly over the registration tabs.

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California limits frame height — 23 inches for passenger cars, 27–31 inches for trucks by weight — and body lifts to 5 inches above the frame.

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Off-road light bars are legal to mount in California but must be covered with an opaque hood and switched off whenever the vehicle is on a highway.

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California's lowering rule: nothing on the vehicle (except the wheels) may sit lower than the lowest point of any wheel rim.

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Underglow is legal in California, including while driving, if diffused and dim (≤0.05 cd/sq in, ≤720 sq in total), not red toward the front, and not flashing.

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California requires fenders, covers, or devices — including flaps or splash aprons — that minimize spray to the rear and are at least as wide as the tire tread. There is no inch limit on protrusion.

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Transparent material is allowed on the topmost portion, with its bottom edge at least 29 inches above the undepressed driver's seat, and it may not be red or amber. Because the material must be transparent, a printed or opaque banner is not legal in California — only a clear tint band.

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Front side windows: minimum 70% VLT. Rear side and back windows: any darkness.

Limits, exceptions & statute →