Simi Valley, CA Noise Ordinances: Vehicle Noise (2026)

Vehicle exhaust and stereo noise on public roads is preempted by the California Vehicle Code, which applies uniformly in unincorporated Ventura County. Vehicle Code Section 27150 requires every motor vehicle to have an adequate muffler in constant operation and properly maintained to prevent excessive or unusual noise, and prohibits exhaust cutouts or bypasses. Section 27151 makes it unlawful to modify an exhaust system to amplify or increase noise beyond the limits for that vehicle type; for vehicles with a manufacturer's gross vehicle weight rating under 6,000 pounds (other than motorcycles), a sound level of 95 dBA or less when tested under the applicable SAE standard complies. Loud car audio is addressed by Vehicle Code Section 27007, which bars a driver from operating a sound amplification system that can be heard outside the vehicle from 50 feet or more while the vehicle is on a highway, except to request assistance or warn of a hazard. The County does not layer a separate decibel ordinance on top of these state standards; the Vehicle Code is enforced by the California Highway Patrol and the Ventura County Sheriff.