Top 5 Illegal Car Mods in California

As you know, car modifications are fun. They make your car different from all the other cars on your block and make it stands out in the crowd. Most importantly, they make driving a pleasure. And who doesn’t want to do that?

Illegal Car Mods in California
Photo by: pereslavtseva

But before you think about all the amazing ways you can modify your car, there is one thing you need to be aware of — laws. There are laws in the United States about modifying your car. Here’s the top five illegal car mods in California that you should know.

California car modification laws 2022

California has always had a thriving car culture. After all, the Golden State is home to the headquarters of major automakers like Toyota and Nissan and many smaller shops and racing teams.

With so many people working in the auto industry in California, it’s no surprise that there are some of the strictest laws on car modification in the country.

Car mods usually mean threats to the environment and safety. Most of these regulations are put in place to protect drivers from unsafe modifications that could lead to an accident or environmental damage. However, some illegal modifications can threaten public safety.

Illegal car mods in California

If you live in California and want to modify your car or truck, you must know which modifications are legal before making any changes to your vehicle. The following car mods are illegal in California:

  1. Exhaust systems that exceed 95 decibels
  2. Engine tune that is not certified by the California Air Resources Board (CARB)
  3. Front windshield and front side windows with less than 70% VLT
  4. Underglow system emits more than the allowed 0.05 candela/square inch
  5. Nitrous oxide system without CARB certification

If you’ve altered your car, you may have to change some of those alterations depending on what else you’ve done. Check out the following list if you plan on making more changes:

1. Exhaust modifications

Exhaust modifications are a popular choice for many car enthusiasts. There are many different ways you can modify your exhaust system, from changing the muffler to adding an aftermarket exhaust system. Changing the muffler will give you a little more power and make your car sound a lot better!

You must check local laws before installing an aftermarket system or any other type of modification as some states have strict noise or emission laws which may affect what you can do with your vehicle!

Having an aftermarket exhaust systems that exceeds 95 decibels when tested under SAE J1492 is one of the illegal car mods in California. This is equivalent to a lawnmower or hairdryer.

27150(a): Every motor vehicle subject to registration shall at all times be equipped with an adequate muffler in constant operation and properly maintained to prevent any excessive or unusual noise, and no muffler or exhaust system shall be equipped with a cutout, bypass, or similar device.

27151(a): A person shall not modify the exhaust system of a motor vehicle in a manner that will amplify or increase the noise emitted by the motor of the vehicle so that the vehicle is not in compliance with the provisions of Section 27150 or exceeds the noise limits established for the type of vehicle in Article 2.5 (commencing with Section 27200). A person shall not operate a motor vehicle with an exhaust system so modified.

2005 California Vehicle Code Sections 27150-27159 Article 2. Exhaust Systems
Photo from REM Audiology

Senate Bill 1079

In 2022, the California State Legislature approved a pilot program to use sound-activated cameras to catch drivers who are violating the state’s noise pollution laws. The pilot program will be tested in six different cities from January 2023 to December 2027.

The California Vehicle Code stipulates that modified car exhaust systems must not be louder than 95 decibels.

Assembly Bill No. 1824

The new bill did not change the less than the 95-decibel requirement for exhaust noise but made it clear that violators will be fined immediately instead of after 30 days.

2. Engine modification

Engine modification is the process of changing the engine of a car to improve performance, fuel economy, and emissions, or to alter its sound. There are many types of engine modifications, ranging from simple bolt-on parts to more complex engine swaps.

Engine tuning refers to adjustments that can be made to the engine’s air/fuel mixture (which affects power output and emissions) and ignition timing (which affects fuel economy). This can be done by remapping the ECU (Electronic Control Unit) to change ignition timing and fuel delivery settings.

Any tune that is not certified by the California Air Resources Board (CARB) is considered one of the illegal car mods in California that will cause an emissions inspection failure.

This policy applies to all OBDII-equipped cars and trucks MY1996 and newer.

CARB California smog check program

The California Air Resources Board (CARB) is the “clean air agency” of the government of California.

Smog inspections are required for all vehicles registered in California. The program, administered by the Bureau of Automotive Repair (BAR), helps to ensure that vehicles meet emissions standards. Smog checks are required twice a year when you register or renew registration for your vehicle.

The program identifies vehicles with excess emissions and reduces pollution in California. As an emissions control device, the ECM requires a CARB Executive Order number to be modified.

Starting in 2021 smog checks will now test whether the ECM has been altered beyond OEM settings, through non-CARB-approved calibrating (tuning). To avoid failing the test, you can remove the modified ECM by simply restoring it to the OEM standard. This process is called “flashing back”.

If you want to avoid problems with the new rule, follow it. If you’re asking yourself, “Is engine tuning worth it?” you already know the answer.

3. California window tint laws 2022

Window tinting is a popular car modification that provides protection from the sun and offers privacy. It is a great way to darken and protect your vehicle’s interior. But it can also be illegal if it’s too dark.

The VLT percentage refers to how much light is allowed to pass through the glass. A VLT of 70% means that 70% of the light coming through the window is blocked. The lower the VLT percentage, the darker the window.

In California, the front windshield and front side windows must have a 70% VLT or less. There are no restrictions on how dark the tint on rear or back side windows can be. However, red, amber, or blue tints are not allowed.

If you’re interested in purchasing a car with darker tinted windows, make sure it meets all safety regulations before taking ownership.

A person shall not drive any motor vehicle with any object or material placed, displayed, installed, affixed, or applied upon the windshield or side or rear windows.

Vehicle Code 26708

Aside from using the prescribed window tint colors, the windshield should be free from obstructions too. This means no stickers or other decorations on their front side windows, as well as torn, bubbled, or worn window tint film that can obstruct the driver’s view is forbidden and must be repaired or removed.

4. Car body modifications

Car body modification is the process of modifying the appearance of a car. It can involve anything from simply changing the color or trim of a car to completely remaking the bodywork to show it off in a different way.

Some common modifications are:

  1. Neon lights (the colored lights on the underbody and around the windows)
  2. Changing car height (raising or lowering the suspension, typically done with coil-overs or lowering springs)

Neon underglow

Underglow is legal in California and Texas, but it must meet certain restrictions. The lowest allowed emitting brightness of a light is 0.05 candela per square inch. All aftermarket lights must not be installed within 12 inches of the vehicle’s required lights as well.

We recommend avoiding blue, red, and green colors are prohibited on any aftermarket lights including underbody glow. No flashing lights are permitted either.

If your underglow system emits more than the allowed 0.05 candela/square inch, you may use white and amber lights in front and red lights in the back.

5. Nitrous oxide system

Nitrous oxide (N2O) is an inhalable anesthetic gas. When used in a dental office, it gets you high. When used in a car, it provides a burst of power.

When activated, nitrous oxide allows more oxygen into your engine to burn more fuel for more power, resulting in increased horsepower and torque.

The amount of extra power depends on how much nitrous you use and how much air is entering the engine at that time. The more air entering your engine, the less power NOS will provide because there’s already enough oxygen present to burn all of that fuel.

Any person who possesses nitrous oxide or any substance containing nitrous oxide, with the intent to breathe, inhale, or ingest to cause a condition of intoxication, elation, euphoria, dizziness, stupefaction, or dulling of the senses or for, in any manner, changing, distorting, or disturbing the audio, visual, or mental processes, or who knowingly and with the intent to do so is under the influence of nitrous oxide or any material containing nitrous oxide is guilty of a misdemeanor.

California Penal Code 381b

In California, it is illegal to have a nitrous oxide system in your street vehicle unless it has been CARB certified.

Nitrous oxide is legal in California when used on race tracks by authorized teams during sanctioned races only (not street racing) provided that they are labeled with a CARB number.


This article discussed the most common illegal car mods in California. If you want to mod your car and drive it around the state, you should know what is legal and what is not. These car laws exist for a reason—many of them are in place to regulate pollution, protect citizens from potential danger, or just prevent the driver and those around him or her from finding out the hard way how they work.

It’s like the tagline says: know your legal rights and limitations. Doing illegal car mods could get you a hefty fine. Even minor infractions can result in a high fine, so it might be better to stick with what’s legal.

Read more: Illegal Car Mods in Texas – 9 Facts You Should Know



Leave a Comment