How many catalytic converters do you need to pass emissions?
There isn’t a universal number you must meet to pass an emissions test. The key requirement is that your vehicle’s exhaust after-treatment system, including catalytic converters, performs within the legal standards for your market. Most cars have one or two catalytic converters, but the exact setup depends on the vehicle’s design and year.
What pass/fail hinges on, not a fixed converter count
Emissions tests evaluate how clean the exhaust is and whether the catalytic system and related sensors are functioning properly. In the U.S., federal rules plus state programs set allowed levels for pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides. Many cars shipped after 1996 use OBD-II monitors that must show readiness, and some states require a tailpipe test. The number of catalytic converters is not the criterion; the converter(s) must be working and the system must meet the standard.
Common catalytic converter configurations
Vehicle makers use a few typical exhaust designs. The exact number of catalytic converters varies by engine, model year, and emissions regulations. Here are the usual setups you might encounter.
- One catalytic converter: Some smaller or older vehicles rely on a single main catalyst in the exhaust path.
- Two catalytic converters: A close-coupled (pre) converter near the engine and a second main converter downstream for additional purification.
- Multiple converters across banks: Some larger engines or trucks employ more than two catalysts, or separate converters for different exhaust banks to meet strict standards.
Configuration varies by vehicle; if you’re unsure how many catalytic converters your vehicle has, check the owner’s manual or a repair guide for your model.
Tips to help ensure you pass the test
Rather than focusing on the number of converters, the practical goal is to keep the catalytic system and related components in good working order. The following steps help improve the odds of passing.
- Maintain the catalytic converter and replace failing units or sensors as needed.
- Fix exhaust leaks, damaged pipes, or corroded hangers that can affect catalytic efficiency.
- Address sensor issues (oxygen sensors, mass air flow sensor) and ensure the engine runs properly to avoid contaminating the catalyst.
- Make sure the vehicle’s OBD readiness monitors show as ready before a test, when applicable.
Note: Tampering with emissions equipment or removing catalytic converters is illegal in most jurisdictions and can lead to penalties and failed tests.
If your vehicle fails: next steps
If a test reveals poor catalyst performance, seek a qualified repair shop to diagnose the cause, which may include the catalyst itself, sensors, fuel system, or ignition problems. Some states offer a test-and-repair program to help bring vehicles into compliance.
Summary
The number of catalytic converters isn’t the controlling factor for emissions eligibility—the system’s effectiveness is. Vehicles generally have one, two, or more catalysts depending on design, but passing hinges on the catalytic converters and related components meeting regulatory standards and functioning correctly. Regular maintenance and timely repairs are the best path to staying compliant and avoiding test failures.
How many catalytic converters are required?
Most cars usually have one single convertor, but cars with dual exhaust systems tend to have two converters. Some vehicles also have more than two converters, which are generally required to meet emission standards. Can you have zero catalytic converters, though?
Can you pass emissions with a P0420 code?
Yes, a P0420 code will likely cause a vehicle to fail an emissions test because it indicates a faulty or inefficient catalytic converter, which is a key component of the emissions system. In most states, an illuminated "check engine" light from a P0420 code is an automatic failure for emissions inspection, regardless of the actual emissions levels. The code means the catalytic converter is not effectively cleaning the harmful pollutants from the exhaust.
Why a P0420 code fails emissions
- Catalytic converter inefficiency: The P0420 code means the catalytic converter is not working as efficiently as it should, and a failing converter cannot adequately clean harmful gasses.
- Check Engine Light: Most modern vehicles will fail an emissions test if the "check engine" light is on, and the P0420 code is what turns that light on.
- Reduced pollution control: A faulty converter leads to a greater release of pollutants into the atmosphere.
- State-specific regulations: Some states have stricter rules and may even have their own "readiness monitors" that must be completed before a test, and a P0420 code can prevent these monitors from becoming ready.
What to do
- Get it fixed: While the car may still be drivable, the P0420 code is a sign of a serious problem that will cause you to fail inspection and can lead to decreased fuel economy and potential engine damage over time.
- Use an emissions system cleaner: In some cases, a fuel/exhaust system cleaner may help clean out the system and temporarily fix the problem, potentially allowing you to pass the test, though it is not a permanent fix.
- Have it professionally diagnosed: A proper diagnosis is the best way to determine if the catalytic converter itself is bad, or if the problem is caused by another component like an oxygen sensor or a leaky exhaust.
What is a scrap catalytic converter worth?
A scrap catalytic converter can be worth anywhere from $25 to over $1,000, but the price depends on the make, model, and condition of the converter, particularly the amount of precious metals (platinum, palladium, and rhodium) inside. Converters from hybrid vehicles and certain foreign cars are often more valuable, while aftermarket units are worth significantly less.
Factors that influence the value
- Precious metal content: The primary factor is the concentration of platinum, palladium, and rhodium. Converters from hybrid vehicles often have more of these valuable metals, says RRCats.com.
- Vehicle make and model: OEM (Original Equipment Manufacturer) converters from certain cars are more valuable than others. For example, converters from hybrid vehicles can be worth $400–$1,000 or more, notes RRCats.com.
- Condition: The converter must be intact, with the internal ceramic structure full and not broken or hollowed out. An intact unit is worth much more than a broken one, where the precious metals may be lost.
- Aftermarket vs. OEM: Aftermarket converters have significantly less precious metal and are worth much less (sometimes as little as $5) compared to OEM units.
How to get an accurate price
- Contact a scrap buyer: Companies specializing in catalytic converter recycling can provide an accurate quote.
- Provide photos: Many buyers ask for pictures, especially of the serial number stamped on the converter, to help with an accurate evaluation.
- Check current market prices: The value of precious metals changes, so checking daily prices on recycling websites can give you an idea of the current market, says RRCats.com.
Can you pass emissions with a bad catalytic converter?
If the car was originally equipped with a catalytic converter than it will not pass an emissions test without it. Because there are two parts to the test. One is a visual inspection of all smog related equipment, and the other is the actual test. With the cat missing, it will not pass either test.
