A catalyst is a part of a car engine that removes poisonous carbon from engine emissions. When the catalyst is dirty or clogged, the check engine light will come on to warn you that something is wrong. By catching the problem early, and using a cleaning additive in the gas tank, you should be able to fix the catalyst and avoid having to buy a replacement part!
Steps
Part 1 of 2: Self-diagnose the problem

Step 1. Purchase or borrow an on-board diagnostic scanner (OBD-II)
Scanners are made to "read" problems that are reported by the check engine light. They are available to buy online and at most auto parts stores. If you don't want to buy one, consider borrowing his from a friend, or take the car to the mechanic.
- When shopping around for a scanner, make sure the one you're buying works with your car brand. Some scanners are made to work only with specific brands!
- Scanners have become quite accessible in recent years. The most basic one that only produces a trouble code will cost between $ 20 and $ 30.

Step 2. Plug the OBD-II scanner into the port under the dash
Plug the scanner into the port under the dash on the driver's side. Check the user manual if you are not sure where the port is located.
If you have trouble finding the port even after checking the manual, use a check lamp under the steering wheel and along the bottom of the dash on the driver's side

Step 3. Turn the car key without starting the engine
This will turn on the electricity in the car and activate the scanner. Wait until the scanner turns on and charges, and keep the car running with the engine off while the scanner is plugged in.
Do not start the engine while using the scanner. This could interfere with the scanner and cause it to malfunction

Step 4. Enter the make, model and VIN of the car into the scanner
Once you've turned on the scanner, a pop-up screen will appear asking for more information about the car. Carefully type all the required information on the keyboard to ensure that the scanner is reading accurately.
- The VIN for most cars is located on the driver's side, and you can see it peeking in the lower right corner on the outside of the windshield.
- Sometimes the scanner will ask for the motor type. If you don't know what kind of engine the car has, check the owner's manual.

Step 5. Wait for the reader to produce a trouble code
After a few seconds, the reader will produce a code or some codes that it will have gathered from the car's data. Typically this will be a set of numbers and letters. Write them down or take a photo of the codes on the scanner for future reference.
Some high-end scanners might display 2-3 words indicating where the problem originated or which part of the code corresponds to

Step 6. Check the user manual or online to make sure the catalyst is the source
Search online for the code that produced the scanner, or check your user manual for a set of known trouble codes. Make sure the code corresponds to a problem with the catalyst and not a problem with another part of the car.
If you are having trouble locating the code information, try searching by the car's model and grim reaper, the word "forum," and the error code. This could lead you to more car forums where drivers discuss problems they have had with their cars
Part 2 of 2: Using a cleaning additive

Step 1. Decide which cleaner is correct for your engine
Different cleaners offer different benefits, and most will depend on the type of car you drive. Check online reviews to find the best cleaner for your make, model, and type of engine.
Engine type is very important when selecting a cleaner. Some are formulated specifically for diesel vehicles, while others are designed for gasoline cars

Step 2. Wait until the tank has about 15 liters (4 gallons) left
Some products require more gasoline than others. As a general rule of thumb, the plan is to have a few gallons of gasoline before adding the cleaner. Always read the directions on the packaging before adding the product to the tank!
If the check engine light appears when the tank is almost empty, get the correct amount of gasoline for the cleaner before adding the product to the tank

Step 3. Pour the cleaner into the gas tank
Depending on the brand you use and how much gas is in the tank, you will have to use part or all of the bottle. The cleaner will mix with the gasoline and run through the catalyst as you drive.
Make sure to carefully follow the directions on the bottle. The correct mixture of cleaner and fuel will ensure that the engine continues to run properly

Step 4. Fill the tank with gasoline when it is almost empty
Drive the car normally until the tank is almost "empty" and then fill it as you normally would. Once you fill up the tank, the car should be running normally, and you might even notice that the engine runs better!
If you're in a rush and don't want to wait until your tank is empty, make sure you drive at least 10 miles (16 km)

Step 5. See a mechanic immediately if the check engine light comes back on
In the United States, it is against federal law to remove a catalyst from a car. If the light comes back on, immediately take the car to a licensed mechanic to diagnose any underlying problems or have the faulty catalytic converter replaced.
Your mechanic may recommend replacing the catalyst, or a different product that works better with your car
Warnings
- Do not remove the catalytic converter from the engine for any reason.
- Wetting the part with water or solvent cleaner can cause irreparable damage.