California’s exhaust laws are among the strictest in the U.S., focusing on environmental protection. These rules affect many vehicle owners, and non-compliance can lead to fines or failed inspections. Understanding these regulations helps avoid penalties. Knowing California’s requirements for exhaust systems is beneficial when buying cars, considering aftermarket parts, or preparing for smog checks. This article covers the main points.
Noise Thresholds
California regulates vehicle exhaust noise. California Vehicle Code Section 27150 requires every motor vehicle with an internal combustion engine to have an adequate muffler, maintained and working, to prevent excessive or unusual noise.1California Public Law. California Vehicle Code Section 27150 (2025) This law also bans mufflers or exhaust systems with cutouts, bypasses, or similar devices.
California Vehicle Code Section 27151 specifies noise limits.2California Public Law. California Vehicle Code Section 27151 (2025) For motorcycles, these limits depend on the manufacturing date:
- Manufactured before 1970: 92 decibels (dBA)
- Manufactured after 1969 and before 1973: 88 dBA
- Manufactured after 1972 and before 1975: 86 dBA
- Manufactured after 1974 and before 1986: 83 dBA
- Manufactured after 1985: 80 dBA
These measurements are taken at 50 feet from the center of travel.
For passenger cars and light trucks under 6,000 pounds (gross vehicle weight) manufactured after 1974, the noise limit is 95 dBA, tested under California Highway Patrol (CHP) procedures.3Justia Regulations. California Code of Regulations, Title 13, Section 1036 – Passenger Cars and Light Trucks and Buses Law enforcement can also issue citations based on an officer’s judgment of “excessive or unusual noise,” even without a decibel meter.
Emissions Compliance
California also strictly controls chemical pollutants from vehicle exhaust. The California Air Resources Board (CARB) sets and enforces these emissions standards. Vehicles registered in California must meet these requirements, which affects the legality of exhaust systems.
The On-Board Diagnostics (OBD) system (OBD-II for 1996+ model year vehicles) is important for emissions compliance. If a problem occurs that could increase emissions, the “Check Engine” light turns on. A fully functional OBD system without trouble codes is required to pass the Smog Check Program. Modifications interfering with the OBD system can cause a Smog Check failure.
Aftermarket exhaust parts that could affect emissions need an Executive Order (EO) number from CARB. Vehicle Code Section 27156 makes it illegal to install, sell, or advertise any device altering a required pollution control system unless CARB has exempted it.4California Public Law. California Vehicle Code Section 27156 (2025) Many aftermarket exhaust components without a CARB EO number for the specific vehicle are not street legal in California.
Official Inspections
California uses Smog Checks, managed by the Bureau of Automotive Repair (BAR), to ensure vehicles meet noise and emissions standards. Most vehicles manufactured in 1976 or later need a Smog Check every two years, when changing ownership, or when first registering in California.5California DMV. Smog Inspections
A Smog Check includes visual and functional inspections. Visual checks confirm all required emissions-control components are present and unmodified. Functional checks assess systems like the On-Board Diagnostics (OBD) and “Check Engine” light. Many vehicles also have a tailpipe emissions test.
Smog Checks are done at state-licensed stations. If a vehicle passes, the station sends a compliance certificate to the DMV. If it fails, the owner receives a Vehicle Inspection Report (VIR) explaining why. The vehicle cannot be registered until it’s repaired and passes a retest.
Tampering Offenses
California law strictly prohibits illegal tampering with vehicle exhaust systems that affects pollution control or noise levels.
Removal of Catalytic Converters
Catalytic converters reduce harmful exhaust pollutants. Removing a catalytic converter or replacing it with a non-exempt “test pipe” or straight pipe is illegal. Health and Safety Code Section 43008.6 states that no one can install, sell, or advertise any device that changes a required motor vehicle pollution control system unless CARB has granted an exemption.6California Public Law. California Health and Safety Code Section 43008.6 (2025)
Altered Mufflers
Modifying a muffler to be louder than the original, or installing an aftermarket muffler that doesn’t meet California’s noise standards, is illegal. Mufflers must effectively dampen noise and not be altered to create excessive sound.
Other Unauthorized Modifications
It is illegal to disconnect, modify, or alter any required pollution control device in California. Installing unapproved aftermarket parts that affect emissions or the operation of emissions control systems is also prohibited. The vehicle’s entire emissions control system, as certified by the manufacturer and CARB, must be intact and working correctly.
Fines and Penalties
Violating California’s exhaust laws can result in fines and other penalties. The specific consequences depend on the type of violation (noise or emissions) and if it’s a repeat offense.
Fines can be issued for violations like inadequate mufflers, excessive noise, or illegally modified exhaust systems. Base fines might seem low, but with added fees and assessments, the total cost can be several hundred dollars or more. For instance, a $25 base fine for loud exhaust can end up costing around $193.
Emissions violations also carry penalties. Failing a Smog Check prevents vehicle registration renewal, making vehicle operation illegal. CARB can issue large civil penalties for emissions control law violations, like selling or installing uncertified aftermarket parts. Tampering with emissions devices or selling non-compliant parts can lead to penalties up to $37,500 per violation (Health and Safety Code Section 43016).7California Public Law. California Health and Safety Code Section 43016 (2025) Willful violations for uncertified parts result in the maximum fine.
Many exhaust and emissions violations have specific penalties. For example, California Vehicle Code Section 42001.14 sets fines for tampering with pollution control devices at $50-$100 for a first conviction, and $100-$250 for subsequent convictions.8FindLaw. California Vehicle Code – VEH § 42001.14 These base fines are increased by state and county assessments and court fees. General vehicle code infractions also carry fines that escalate with repeat offenses.
Exceptions and Special Circumstances
California’s exhaust regulations have some exceptions for specific vehicle types, uses, or conditions.
Vehicles manufactured before the 1976 model year are exempt from the biennial Smog Check program.9Bureau of Automotive Repair. Collector Cars and Smog Check Exemptions This exemption is for testing only; they may still need to have original emissions equipment if they came with it. These older vehicles must also follow noise rules and not produce excessive smoke.
Vehicles designed only for off-highway use, like dedicated off-road motorcycles or ATVs not registered for road use, follow different rules. However, if an off-highway vehicle is modified for or used on public roads, the standard on-road regulations apply.
Rules also exist for vehicles in sanctioned competitive racing events. The prohibitions against modifying pollution control devices might not apply to vehicles used only off-highway or for racing. A racing vehicle, as defined by California Vehicle Code Section 500, is used only in speed contests and is not meant for highway use.
Emergency vehicles might have different exhaust system rules, especially for noise, because of their operational needs. This is not a complete exemption from all equipment requirements.
If an original equipment manufacturer (OEM) exhaust part is not available, CARB might allow specific replacements that meet performance standards. The Bureau of Automotive Repair’s Consumer Assistance Program (CAP) offers financial help for emissions repairs or for retiring high-polluting vehicles to eligible consumers.10Bureau of Automotive Repair. Consumer Assistance Program (CAP)