California’s vehicle exhaust regulations manage noise and air pollution. These laws establish clear directives for vehicle owners regarding the sound output and emissions control equipment of their cars. The regulations cover everything from how loud an exhaust can be to the specific equipment required to keep emissions in check.
California Exhaust Noise Limits
California law sets a distinct limit on how loud a vehicle’s exhaust can be. Governed by California Vehicle Code sections 27150 and 27151, the rules are designed to control excessive vehicle noise. For most passenger cars and motorcycles, the exhaust system cannot produce a sound level higher than 95 decibels (dBA).
Law enforcement measures exhaust sound levels using a meter, following a standardized testing procedure where the engine is held at a certain RPM to ensure readings are consistent. For noise violations, officers can issue a correctable “fix-it” ticket.
Prohibited Exhaust System Alterations
The state explicitly forbids certain modifications to a vehicle’s exhaust system. This includes common modifications such as muffler deletes, where the muffler is completely removed, as well as the installation of exhaust cutouts or bypasses that allow exhaust gases to circumvent the muffler. Whistle tips, which are designed to create a loud whistling sound, are also strictly prohibited.1FindLaw. California Code, Vehicle Code – VEH § 27150.3 | FindLaw
Beyond noise, alterations that compromise a vehicle’s emission control system are also illegal. It is against the law to tamper with or remove a catalytic converter.2California Public Law. California Vehicle Code section 27156 (2025) Any replacement catalytic converter must be a unit approved by the California Air Resources Board (CARB), and many aftermarket exhaust systems must have a CARB Executive Order (EO) number.3California Air Resources Board. California Racing Vehicles: Aftermarket Parts & Executive Orders This number certifies that the part has been tested and does not negatively impact emissions.
Exhaust Integrity and Smog Check Rules
A vehicle’s exhaust system is a focal point of the California Smog Check inspection. During the visual portion of the test, inspectors examine the exhaust for compliance, verifying the presence and integrity of required components like the catalytic converter and oxygen sensors. Any signs of tampering, such as illegal welds indicating a removed component, will result in an immediate failure.
The system must be completely sealed and free of any leaks from the engine to the tailpipe. A leak can allow harmful gases to escape before they are treated by the catalytic converter, leading to a failed emissions test. A compromised or illegally modified system will prevent a vehicle from passing its smog inspection, which is required for registration renewal.
Consequences for Illegal Exhaust Systems
Violating California’s exhaust laws can lead to several penalties. For excessive noise, a driver will typically receive a correctable “fix-it” ticket. Penalties for tampering with emissions control systems are much more severe. Modifying or removing equipment like a catalytic converter can lead to substantial fines.
In these cases, a driver may be ordered to a Bureau of Automotive Repair (BAR) Referee station for a comprehensive inspection. Failure to address any exhaust violation can result in a hold on the vehicle’s registration renewal.
Resolving an Exhaust Violation Ticket
If you receive a correctable “fix-it” ticket for an exhaust violation, there is a specific process to follow. The first step is to have the vehicle repaired to meet state standards. This may involve installing a compliant muffler, replacing an unapproved aftermarket part with one that has a CARB EO number, or reinstalling a factory-certified catalytic converter. It is important to keep all receipts and documentation from the repair shop as evidence of the work performed.
After the repair, you must get the correction certified. This certification can be done by the same law enforcement agency that issued the citation or at a designated inspection station. The officer or inspector will visually check the repair and sign off on the ticket itself, confirming that the vehicle is now in compliance. This signed-off citation serves as your proof of correction.
Finally, you must provide this proof to the court by the deadline specified on the ticket. This typically involves paying a dismissal fee to the court clerk, who will then clear the violation from your record.