If the sluggish engine performance for the past six months hasn’t been a big enough hint, now the check engine light flashes on, and you get that dreaded P0420 (or PO430) code readout stating that your number 2 manifold catalytic converter is having issues.
Catalytic Converters contain precious metals that help remove toxins from the exhaust of gasoline engines. In doing so, they reduce harmful emission levels.
Those rare metals (such as platinum) drive up the price of this part.
Over time, the carbon build-up can interfere with the metal’s ability to clean your exhaust, creating error codes.
Recently I asked a small muffler shop if they could just delete my catalytic converter. “Not unless I want to pay a $10,000 fine,” he said.
So it comes down to fixing your current cat or ponying up the money to replace it.
Here are some easy cleaners you can try. I’ve done the research to find the ones that have the best chance of working.
Pro Tip: Use a High-Octane Premium-grade Fuel With These Cleaners
The Best Catalytic Converter Cleaners Comparison
My Favorite: Cataclean
Cataclean is one of the most exciting products to hit the market. They promise a reduction in hydrocarbon emissions by up to 50%.
It’s also compatible with gas, diesel, and hybrid vehicles (all of the ones on this list will work for gas and hybrid cars that use gasoline).
Compatible with both pellet and honeycomb-style converters, this one is designed to get a deep clean. Repeated use only improves performance further.
Not only does it help to clean the catalytic converter, but it also clears off those oxygen sensors, getting the carbon off your engine valves, and cleaning the spark plugs.
The end result is an engine that not only runs better but is also less likely to foul up or create carbon-related repairs down the road.
For our readers in California, this one complies with VOC and is legal to use in California, making it easier to pass the emissions tests.
Once you add it to a full tank, drive until the fuel tank is nearly empty. At the next refill, clear the OBDII codes and drive at least 50 miles. If the codes clear, you may have solved the problem.
Cataclean works by creating oxygen and Carboxylic acid to interact with the carbon and remove it from the system.
CRC “Guaranteed To Pass” Formula
CRC makes some excellent products. I just used their GDI intake valve cleaner on my GMC, and it worked like a charm. It only took me about 15 minutes and saved me nearly $100 on the mechanic’s fee.
They position themselves as the “legitimate” choice, and you will find their products in every auto repair shop.
With their guaranteed-to-pass-emissions-test formula, they are offering the maximum legal amount of cleaner allowed by law.
When you run this through your car, it is designed to remove gunk from the fuel injectors and carbon deposits from your valves, the head of the piston, and your exhaust system.
The use is simple. Run one bottle for up to 16 gallons of gas. Dump it in, run that tank through your car and then Refill your tank. Generally, the check engine light will go off after 50 or so miles, and you are ready for the emissions test.
The results are so excellent that you’ve got some folks dumping a can in every time they refill. While I think that is overkill, you could do it every 3,000 miles or three months to improve your fuel economy.
In my opinion, I’m hard-pressed between whether Cataclean or CRC’s product will work better. They are both excellent products. Some folks have mentioned in forums that they used one or the other first, and then the other and the second one worked.
Whether that means one product is better, or that their system simply needed two bottles of cleaner, is tough to know.
This is the only one with a money-back guarantee. Keep in mind that if you don’t pass the test, you only get your refund after you have receipts for the repairs.
I highly doubt many of us are going to get copies of our receipts and send them in. It’s a pretty safe bet for CRC to make.
Solder-It Cat-1 Cleaner
Here is an oldie but goodie. Billing themselves as the “original,” their instructions continue to advertise that you can dump it straight down the carburetor for faster cleaning action.
Most of us with fuel injection systems will need to put it into the gas tank and let it run through. Near the end of that tank of gas, the check engine light should go off.
As with all of these products, sometimes it takes a couple of tries. Some folks run this and then run one of the other products. Anecdotally, I’ve heard of folks running two of them in one tank with no adverse problems.
Fascinatingly enough, the MSDS sheet only mentions N-butane as the ingredient. After digging into the company’s profile, I discovered that Solder-it specializes in providing butane and soldering equipment.
This is a side product they create.
Somehow, they figured out that slamming the car with butane can help remove carbon deposits. However, it seems like this brand misses some of the complex chemical reactions that the other brands offer.
Red Line (60103) Complete SI-1 Fuel System Cleaner
In college, I drove nothing but ancient, high-mileage cars. As a result, I used Red Line’s fuel cleaner in most of them. Once a quarter or before a long road trip, I’d drop a bottle in the tank. It’d clean the injectors, boost performance, and improve fuel efficiency.
Most of the cleaners on this list emphasize high-temp cleaning. They are activated in the combustion chamber, and the fumes are used for their cleaning action.
With this cleaner, it contains both high temp and low temp cleaners. This lets it clean the injectors and fuel lines, removing varnish and improving the flow. Then, it activates under heat and becomes a powerful oxygen sensor and cat converter cleaner that removes carbon from spark plugs and your cylinder heads.
They don’t advertise it heavily for its exhaust system cleaning powers, but it is a high effect cleaning agent for the exhaust system.
The reason why SI-1 works so well is that it contains a high concentration of PEA (polyether-amine ). Since 1979, PEA has been one of the most reliable detergent additives, and it still works well with new cars and all of their new sensors.
I’ve had cars that were struggling to get up hills, and SI-1 brought them back to life. Plus, it has plenty of anecdotal stories in forums on folks fixing their P0420 errors with it.
My personal experience has me moving this one up higher on the list than most of the others. If you’ve tried every cleaner and are ready to give up, give this one a shot.
Also sold in a Multipack, this is one of the best options for the busy shop to consider.
Oxicat Oxygen Sensor Maintenance Cleaner
Oxicat is one of the only brands to say “we aren’t a mechanic in a can, use us for maintenance.”
For those of us who love our cars and who want to keep fuel efficiency at it’s highest, this is a good option. (Although the Cataclean also recommends use every e months).
This brand might be more popular with owners of high mileage luxury vehicles such as BMWs and Cadillacs. If your OBD-II is giving you the “catalyst system efficiency below threshold” error, this might be a good bottle to grab.
One of the key things about this product is that the manufacturer emphasizes the need for the catalytic converter to be hot and running at operating temperature in order for the product to provide the necessary chemical reaction.
So, for best results, dump a bottle in and go for a 3-hour drive at highway speed.
As an Oxygen Sensor cleaner, it is one of the best, and it has the added bonus of also removing build-up from the Catalytic Converter.
It is also one of the few brands that bill itself as useable for diesel engines.
Hi-Gear makes a lot of different fuel cleaners and additives. This one is marketed to help with engine pinging, to clean the EGR valve and the combustion chamber.
If you are getting that rotten egg smell, this one is a deodorizer to help fix the cat converter and get rid of it.
The downside is that I am struggling to find much on the company, and I had no luck finding their Material Safety Data Sheet, so there isn’t much information on what the ingredients are.
There are quite a few folks who have mentioned using it with positive results. However, until I can get more details on it, I, personally, would go with one of the earlier brands mentioned.
Royal Purple Max-Clean Fuel System Cleaner and Stabilizer 11722
We currently sell a lot of Royal Purple’s synthetic oil for air compressor use. They make a wonderful product that shop owners trust.
This Max Clean is designed to lend better performance for both diesel engines or gas engines. They advertise an engine power increase of 2.6 percent.
They recommend running it once every 10,00 miles. For most folks, that is a twice-a-year use.
Using it is simple. Just put it in your tank and go.
Mac Auto Parts Sledgehammer Run Rite
This product is designed to clean all angles of the fuel system. One of the areas that no one cleans anymore — now that cars are fuel-injected — is the fuel intakes.
These areas can get both varnish and carbon build-up. CRC makes an excellent cleaner for feeding into a brake line in short shots while idling. This removes that build up.
This Sledgehammer Run Rite promises to be a full-system cleanout to boost engine power.
You start by warming up the engine and filling up the tank. Then you dump step 1 into the tank and remove a vacuum hose. Stuff the end of the vacuum hose with a rag and then poke the spray nozzle into it. Give little squirts of the DTI (Direct Through Injector) cleaner while the engine is running.
Ideally, this is going to clean the system from top to bottom.
However, I’m not finding a lot of feedback on this one yet in my research. Mac Auto parts mostly sell to professional mechanics, so it is likely that you aren’t finding many of them talking about their guru juice in forums.
MotorPower Care Catalytic Converter Cleaning Treatment Oxygen Sensor Latest Technology
The MotorPower Care solution reminds me of a lot of the Oxicat.
As with the other ones on this list, it is either going to work or it isn’t.
They have very specific instructions for use, and you might see an improvement with how the other cleaners work by following MotorPower’s instruction.
The key difference is that they recommend running your car for 40 minutes before adding it to the tank. Then, they want you to take it up to highway speeds for 15 minutes and try flooring it a couple of times.
I think that waiting until the engine is warmed before adding any of these cleaners is a stellar idea. However, as we saw with Oxicat, driving for three or more hours is generally what it takes to get the grime out of a Catalytic Converter.
Once it gets all off the gunk, grime, and carbon out of your fuel line and entire exhaust system, your car should produce less carbon monoxide and carbon dioxide.
The difference with this one is that it isn’t sold specifically as an exhaust system cleaner. If you are fighting check engine lights, check out one of the other brands. This one is just a great all-in-one engine cleaner to improve performance and solve stubborn power problems.
Catalytic Converter Cleaner Buying Guide
Will Laquer Thinner Clear Catalytic Converter’s Codes?
Growing up with 1970’s vehicles, it seemed like the solution to every poor-running car was to dump lacquer thinner into it. Scotty Kilmer still recommends dumping one gal of acetone in your Fuel Tank to fix PO420 codes.
The only problem is, catalytic converters processed burned fumes. Once you run the acetone through your engine and combust it, there isn’t a lot of cleaning power available in its fumes.
The difference with these specific cleaners is that they offer chemicals that continue to provide cleaning power after it has been combusted, or the combustion activates the cleaning components that remove carbon deposits.
I’ve always used one of the professional cleaners with detergents, and I’ve reversed a couple of P0420 codes.
I’ve also replaced a couple of converters.
If you have an old car that you don’t care about burning out your sensors, you might give this a try. But I’d be worried about the damage that it could cause, and doubt it would be very effective.
Maybe that’s why Scotty runs a gallon of it through.
Symptom of a Bad Catalytic Converter
Sluggish engine performance, dark exhaust smoke, and the smell of sulfur can be indications of a bad muffler. Additionally, I’ve had them create enough back pressure that causes one side of the engine bank to begin backfiring, causing a check engine light to come on.
There are a few things that can cause a catalytic converter to foul up more quickly. The antifreeze from a bad head gasket can interfere with the system. Leaded gas can also cause a problem.
While most Additionally, hundreds of thousands of miles will add up, eventually forcing the need for replacement, especially if the car hasn’t had a tuneup and won spark plugs are burning fuel inefficiently, pushing unburnt gasses into the exhaust system.
The added heat put out by a bad catalytic converter can be a big symptom. Shooting a temp gun on one and then the other while the car is running will sometimes show you which side is bad.
Failing to repair or replace a bad catalytic converter can lead to other engine problems. I had a vehicle where the heat from the catalytic converter caused the head to hold more heat, leading to bearing failure and ultimately ruining the engine.
It’s something that you want to get repaired sooner rather than later.
Will a Catalytic Converter Cleaner Help My Car Pass the Emissions Test?
Depending on how bad of condition your car is in, it is possible that a quick system cleaning is a good way to get your car to renew their emission test.
The best pass emissions test formula is to switch your car to premium fuel and to run 2 or 3 of these cleaners through during the week leading up to your test over three tanks of fuel. Following that, run a cleaner through your fuel tank at least twice a year.
Is my Catalytic Converter Bad Or Just Clogged?
If you get a P0420 code — Catalytic Converter Below Threshold — it is possible that you have a bad sensor, but more likely that the platinum and other elements have been exhausted.
Clogged catalytic converters can create added problems of difficulty to start and poor acceleration due to the increased backpressure on the engine.
It is possible for the internal components to break down and fall into the bottom of the unit, physically obstructing the airflow. Sometimes you can dislodge those with high acceleration, but more times than not, the converter has to be replaced when it gets this bad.
Can a Bad O2 Sensor Cause a P0420 Code?
The key thing is that a bad oxygen sensor can mimic a bad converter. A lot of times, folks will replace the O2 sensor first, or swapping the O2 sensor between the good converter and the bad one to test it.
An easier test is to shoot a temperature gun on each to see if there is a massive temperature difference between the two.
Will Catalytic Converter Cleaner Work?
Multiple users in forums have shared their success forums of running a cleaner through their car, getting the check engine light to go off, and successfully passing an emissions test. Sometimes the light stays off, and sometimes it comes back on in a thousand miles.
If you are having problems, regular use of a cleaner is a good idea. Run it through the fuel system and extend the life of your vehicle.
What Causes A Catalytic Converter To Fail? (Carbon Build Up)
It is possible that your vehicle is running rich — taking in too much fuel that it is not burning completely.
You want the air-fuel ratio to be optimized to get a clean burn with the least amount of carbon.
Cars that are running rich can clog a converter in a matter of days. If the issue is bad enough, it may require you to take the converter off and soak it in a solvent.
If your car is running rich, it could be a problem with a dirty air filter or problems with a mass airflow sensor or the vacuum lines. Finally, switching the sparkplug out could make a difference and deliver a complete burning of the fuel.
Catalytic Converters should last the lifetime of your vehicle. If you are getting a code P0420, it is likely that another sensor upstream is failing, throwing more harmful emissions into your system. You need to fix this upstream problem.
As you’ve seen from our catalytic converter cleaner reviews, these products clean the entire fuel system from start to end.
Soaking a Catalytic Converter To Clean it
If the miracle in a bottle isn’t working, you can still save thousands if you are willing to do the hard work of removing your catalytic converter.
You need to remove your converter and soak it in a solution of citric acid and water, or lacquer thinner. My favorite idea is to use the industrial-strength Purple Power cleaner.
After a 6 hour soak, you should get most of the carbon deposits loose. Rinse with water and reinstall.
I think Cataclean offers the most innovative exhaust system cleaner with its Carboxylic acid solution. However, I’ve personally had solid luck with the SI-1 from Red Line, and I’m a huge fan.