Catalytic converters usually suffer weeks or months of rich mixtures, misfires, coolant or oil contamination before they stop working properly. The good news is that mild fouling can sometimes be reversed. But remember: no chemical can fix a melted, broken, or heavily clogged substrate. If this is your problem, you need to replace your catalytic converter.
The wise thing to do is to hold off buying parts until you’ve isolated the issue. Exhaust leaks, slow oxygen sensors, and upstream engine faults (misfires, fuel trim errors) can trick the ECU into blaming the converter. Whether or not to replace your cat depends on correctly diagnosing these issues.
If the issue is light hydrocarbon or oil soot, the heat of the catalyst will typically cook it to ash and it will be eliminated even without any kind of chemical additive. But in worse cases, a fuel-tank additive may be used to clean the catalytic converter without removing it.
These fuel tank additives can be effective for removing hydrocarbon and oil-based soot from a mildly coated catalytic converter. These products are designed to clean the entire fuel and exhaust system, including oxygen sensors and the converter itself.
Note that once the problem that caused the issue is corrected, the catalyst will clean itself unless it has overheated to the point that the honeycomb is coated with something that can’t be cleaned away.
If enough coolant containing silicone enters the exhaust system, it can coat both the oxygen sensors and the catalytic converter, rendering them ineffective and requiring replacement.
The catalyst operates at high temperatures (up to 1,600°F), but silicone compounds don’t simply vaporize with heat. They oxidize and form glassy deposits that coat the precious metal surfaces (platinum, palladium, rhodium).
These deposits block the chemical reactions needed to convert harmful gases. Once poisoned, the catalyst loses efficiency and cannot be restored by heat cycling.
After adding the catalytic converter cleaner, do a sustained hot drive. Aim for highway speeds for 15–30 minutes to get the converter fully hot. If the problem is just soot and fuel varnish from short-trip use, this method can sometimes restore flow. However, if the substrate is cracked, melted from misfires, or loaded with oil ash, don’t expect this trick to work.
Warning: Before adding anything to the tank, diagnose the real cause. A rich mix or misfire that sent raw fuel into the cat will foul a freshly cleaned substrate again. Check fuel trims, misfire counters, and look for leaks ahead of the converter.
They can, within limits. Additives help when the converter is merely coated with carbon and the engine is otherwise healthy. However, they won’t repair a collapsed cat or revive its precious metals that have been heat-damaged (catalytic converters contain precious metals that make them subject to theft).
If you have the DIY knowledge and skill, verify the results after treatment. Log the upstream and downstream O₂ sensors during a steady highway drive. On a healthy converter, the downstream signal should be flatter and lower frequency than the upstream data. Otherwise, the converter is still not working properly.
Used as directed, leading brands of catalytic converter cleaners are formulated to be safe for O₂ sensors and catalytic substrates. These are typically solvent blends (often acetone, xylene, and light petroleum distillates), so follow the instructions and make sure to keep them away from ignition sources. Never exceed the recommended concentration.
Important: in some states, removing the catalytic converter for cleaning could be considered tampering. Federal rules also prohibit tampering and the sale of such devices. Never drill, chisel, or “gut” a catalytic converter.
Most catalytic converter cleaners must go into the fuel tank with the level around one-quarter to one-half full. Drive at steady highway speeds for 15–30 minutes to keep the converter hot; heat activates the formula and helps burn off deposits. Follow your product’s instructions for exact fuel level and drive time.
Tip: Use Top Tier fuel, avoid long idles, and hold a steady load. After the drive, clear the code and complete a full OBD-II drive cycle. If the code stays gone, the treatment likely worked.
Most brands target one drive on the same tank, roughly 15–30 minutes of steady cruising. If the ECU took several trips to set the code, it may take several trips to reset the monitor. Give it a few normal drives after the initial run.
There’s no fixed schedule for this. If your car sees mostly short trips, you can do this as a preventive measure. Many fuel-system cleaners suggest intervals around every 3,000–5,000 miles (often with oil changes). That cadence also keeps injectors and intake valves cleaner, which protects the catalyst. Check your product’s guidance.
Two quick checks can guide your next step:
Removing the converter to soak, spray, or pressure-wash can sometimes dislodge loose soot, but it’s risky. Excess water or high pressure can crack the honeycomb, and harsh chemicals can destroy the catalyst. If you try a rinse, use only low-pressure water, and let the cat dry completely before reinstalling. Again: anything that alters or damages the substrate can be considered tampering, so be mindful of that.
A cleaned converter won’t last if the engine keeps feeding it raw fuel, oil, or coolant. Address misfires, correct rich/lean issues, fix exhaust leaks, and confirm stable closed-loop operation. Mechanics who fix a P0420 issue often start there because upstream faults are so often the real problem.
Because additives are inexpensive, it’s reasonable to try a bottle and a hot highway run when your tests suggest mild fouling. But if backpressure is high, O₂ signals show little to no conversion, or you hear rattling, it’s best to put your money toward a replacement part. Remember to use EPA/CARB-compliant parts; mismatched “universal” units can trigger repeat efficiency codes.
“Best” depends on what you’re targeting. Some products focus on the fuel side to clean injectors and intake paths, which improves combustion and reduces soot loading. Others pitch a single pour-in step for both fuel and exhaust paths.
Here, we’ll look at two popular brands: Davico and Cataclean.
This two-step kit combines a fuel-system treatment with a rapid induction deposit aerosol. It aims to clear injector, intake-valve, and induction deposits so combustion returns to normal chemistry, which lowers hydrocarbon loading on the cat. According to DAVICO, their aerosol is low-VOC, quick to use, and safe for O₂ sensors and converters.
Cataclean is a pour-in cleaner for gasoline and diesel. Add it at roughly a quarter tank, then drive 15–20 minutes before refueling. It contains common solvents (acetone, xylene, isopropanol, light petroleum distillates), consistent with strong detergent action.
If data and backpressure tests indicate the substrate is intact and your problem stems from dirty combustion (rich trims, carbon buildup), a product that cleans injectors and the intake, like DAVICO, reduces the load that fouls the cat. If you want a quick solution for light fouling, Cataclean is simple to use. In both cases, follow the label, get the exhaust fully hot, and verify with pre-/post-cat O₂ comparisons over a few drive cycles.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.