Most catalytic converter cleaners are fuel additives you pour into your tank before a fill-up, designed to burn off carbon deposits that reduce converter efficiency and trigger that check engine light. Whether you’re trying to pass an emissions test or restore lost performance, the right cleaner can save you from a costly converter replacement – but the wrong one is just an expensive bottle of solvent. We tested the Liqui Moly Catalytic System Cleaner, Cataclean Fuel & Exhaust Cleaner 2-Pack, and MotorPower Care Catalytic Converter Cleaner 2-Pack to find out which ones actually deliver results.
Quick Comparison
| # | Product | Key Features | Score | |
|---|---|---|---|---|
| 1 |
Liqui Moly Catalytic System Cleaner 300ml Fuel Additive
|
|
7.8 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 2 |
Cataclean Fuel & Exhaust Cleaner for Gas Engines 2-Pack
|
|
7.8 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 3 |
MotorPower Care Catalytic Converter Cleaner 2-Pack
|
|
7.8 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 4 |
Cataclean 16oz Gasoline Fuel & Exhaust System Cleaner
|
|
7.8 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 5 |
Cataclean Fuel & Exhaust System Cleaner 2-Pack 16oz
|
|
7.8 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 6 |
Dura Lube Severe Catalytic and Exhaust Treatment 16 oz
|
|
7.5 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 7 |
Dura Lube Severe Catalytic and Exhaust Treatment 2-Pack
|
|
7.2 ★★★★☆ | Check Price on Amazon Read full review ↓ |
| 8 |
Ciirvoe 3-Pack Catalytic Converter & Fuel System Cleaner
|
|
6.5 ★★★☆☆ | Check Price on Amazon Read full review ↓ |
A 300ml fuel-tank additive designed to clear carbon deposits from injectors, combustion chambers, and catalytic converters in a single treatment. Pour it into your tank before filling up and let normal driving do the work. At $15.34 per bottle, it is one of the lower-cost maintenance options for gasoline engines showing rough idle or sluggish throttle response.
Key Features
- Reduces soot buildup that clogs catalytic converters
- Cleans fuel injectors and combustion chamber deposits
- Improves fuel combustion efficiency
- Lower fuel consumption reduces CO2 output
- Compatible with all gasoline engines fitted with a catalytic converter
✅ Pros
- Single 300ml bottle treats a full tank with no tools required
- Targets three systems at once: injectors, combustion chamber, and catalytic converter
- Low cost per treatment compared to professional fuel system cleaning services
- Suitable across a wide range of gasoline engine types and displacements
❌ Cons
- Results vary depending on severity of existing carbon buildup and may require multiple treatments
- No visible confirmation that the cleaner has worked, requiring before and after diagnostics to measure impact
Why We Chose It
Liqui Moly has a long track record in European markets for fuel system additives, and this product targets the specific problem of catalytic converter clogging alongside injector and combustion chamber deposits in one treatment. The 300ml size is correctly dosed for a standard passenger car tank, removing guesswork. At under $16, it is a practical first step before spending on professional cleaning or replacement parts.
Perfect For
Gasoline car owners noticing rough idle, increased fuel consumption, or a failed emissions test who want a low-cost DIY maintenance step before visiting a mechanic.
A two-bottle kit designed to clean catalytic converters, fuel injectors, and oxygen sensors in a single tank treatment. It targets common check engine codes like P0420 and P0171 that often lead to costly shop visits. Poured directly into the fuel tank, it requires no tools or disassembly.
Key Features
- Reduces hydrocarbon emissions on gas engines by up to 50%
- Cleans fuel injectors and cylinder heads to improve combustion efficiency
- Targets check engine codes P0420, P0430, P0171, P0174, P0300, P0401
- Helps prevent carbon buildup in catalytic converters over time
- Pour-in treatment requires no tools; works in gas, diesel, and hybrid engines
✅ Pros
- Two 16 oz bottles provide two full treatments at roughly $25 per use
- Addresses multiple systems in one application: catalytic converter, injectors, O2 sensors
- 50-state legal with no special equipment needed
- Can delay or avoid expensive catalytic converter replacement if carbon buildup is the cause
❌ Cons
- No guarantee of resolving check engine codes caused by hardware failure rather than carbon buildup
- Results vary depending on engine condition and severity of buildup
Why We Chose It
At $49.95 for two treatments, it costs far less than a shop diagnostic fee alone, making it a reasonable first step before spending money on repairs. It covers more components per application than most single-system fuel additives, cleaning the exhaust and fuel sides simultaneously.
Perfect For
Drivers whose check engine light recently appeared or who are preparing for an emissions test and want to rule out carbon buildup before paying for mechanical repairs.
A fuel-additive treatment designed to clear carbon deposits from catalytic converters and O2 sensors, targeting P0420 and P0430 fault codes. Each 8.45 fl oz bottle treats one full tank of gas, making the two-pack suitable for a two-cycle cleaning protocol. Works with gasoline and hybrid vehicles, so it covers most consumer drivetrains.
Key Features
- Targets P0420 and P0430 check engine codes via fuel system
- Compatible with gasoline and hybrid vehicle engines
- Cleans O2 sensors and EGR system alongside catalytic converter
- Will not repair physically cracked or melted catalytic converters
✅ Pros
- Two-bottle pack supports a full multi-tank cleaning cycle
- Covers O2 sensor and EGR cleaning beyond just the catalytic converter
- Works across gasoline and hybrid platforms without separate formulas
- At roughly $15 per bottle it costs less than a shop diagnostic fee
❌ Cons
- Only effective on intact converters, so physical damage requires a replacement part instead
- Results vary depending on how heavily carboned the system is before treatment
Why We Chose It
The 2-pack format is a practical advantage because a single treatment rarely clears stubborn carbon buildup, and having two bottles removes the need for a second order mid-cycle. Addressing the O2 sensor and EGR valve in the same pour adds value over single-target cleaners. The clear limitation notice about physical converter damage is honest and helps buyers avoid wasting money on the wrong problem.
Perfect For
A driver whose vehicle recently threw a P0420 or P0430 code, passed a physical inspection showing no cracked converter, and wants to attempt a chemical cleaning fix before spending money on parts or labor.
Pour one bottle into a quarter-tank of gas, run the engine, and it targets carbon deposits in catalytic converters, fuel injectors, and oxygen sensors. It addresses several common check engine codes including P0420 and P0300, which often signal catalytic converter or misfiring issues. At $27.93, it costs far less than a diagnostic appointment, let alone a converter replacement.
Key Features
- Reduces hydrocarbon emissions by up to 50 percent on gas engines
- Cleans fuel injectors and cylinder heads to improve combustion efficiency
- Targets check engine codes P0420 P0430 P0171 P0174 P0300 and P0401
- Helps prevent carbon buildup in catalytic converters with regular use
- No tools required, poured directly into fuel tank, 50-state legal
✅ Pros
- Addresses specific OBD-II codes that would otherwise require shop diagnostics
- Compatible with gasoline, diesel, and hybrid engines in one formula
- Simple application with no mechanical knowledge or equipment needed
- Regular use can extend catalytic converter lifespan and delay costly replacement
❌ Cons
- Clears symptoms of carbon buildup but will not fix mechanical failures or sensor damage
- Single-use bottle at $27.93 adds up if used on the recommended quarterly schedule
Why We Chose It
Cataclean targets the catalytic converter directly, which separates it from generic fuel system cleaners that focus only on injectors. The specific list of addressable OBD-II codes gives buyers a concrete way to assess whether this product is relevant to their situation before purchasing. For vehicles failing emissions checks due to carbon accumulation rather than hardware failure, it offers a low-cost first step before committing to repairs.
Perfect For
Drivers whose check engine light shows P0420 or similar emissions-related codes and want to rule out carbon buildup before paying for shop diagnostics.
Cataclean works through your fuel system to reduce carbon deposits on catalytic converters, oxygen sensors, and fuel injectors. A single treatment targets common drivability complaints like rough idle, hesitation, and hard starts. The two-pack gives you enough for two full treatments or two vehicles.
Key Features
- Cuts total hydrocarbon emissions by up to 50 percent
- Removes carbon from catalytic converter, O2 sensors, fuel injectors, cylinder heads
- Addresses power loss, hesitation, rough idle, hard starts, and poor fuel economy
- Compatible with gasoline, diesel, hybrid, and flex-fuel vehicles
- Not suitable for 2-stroke or oil and gas mix engines
✅ Pros
- Broad vehicle compatibility covers gasoline, diesel, hybrid, and flex-fuel
- Two 16 oz bottles cover two treatments or two separate vehicles
- Targets multiple system components in a single pour-in treatment
- May help pass emissions tests by reducing hydrocarbon output
❌ Cons
- Results vary by vehicle age and severity of carbon buildup
- No benefit for 2-stroke engines, limiting use for some equipment owners
Why We Chose It
The two-pack format lowers the per-treatment cost compared to single bottles, making it practical for households with two vehicles or for seasonal maintenance. It covers more of the fuel and exhaust system in one product than most pour-in cleaners, hitting injectors, sensors, and the catalytic converter together. The up-to-50-percent hydrocarbon reduction claim gives it measurable relevance for anyone facing an upcoming emissions inspection.
Perfect For
Owners of older gasoline or diesel vehicles showing early signs of rough idle, sluggish throttle response, or declining fuel economy who want a low-effort maintenance step before committing to a shop visit.
A 16 oz fuel additive designed to clean catalytic converters and exhaust systems before you consider a costly replacement. It targets phosphorus and zinc buildup at the catalyst inlet, which are common causes of catalytic inefficiency. Universal compatibility means it works across gas engine types without modification.
Key Features
- Add anytime to support fuel system and engine performance
- Use before replacing a catalytic converter to assess need
- Protects catalytic system from oil contamination and efficiency loss
- Reduces phosphorus and zinc buildup at the catalyst inlet
- Universal fit for all engine types, may improve fuel economy
✅ Pros
- Cheaper alternative to attempting a catalytic converter replacement first
- Addresses specific chemical culprits like phosphorus and zinc at the catalyst inlet
- Universal compatibility removes guesswork about engine fitment
- 16 oz bottle provides a full treatment dose without splitting
❌ Cons
- Results vary depending on how fouled the catalytic converter already is
- No independent data provided on fuel economy improvement magnitude
Why We Chose It
This product targets a specific and expensive problem: a degraded catalytic converter. At $21.28 it costs a fraction of a replacement converter, making it a practical first step before committing to a repair. The focus on phosphorus and zinc reduction at the catalyst inlet shows a more targeted formulation than generic fuel system cleaners.
Perfect For
Drivers seeing a check engine light related to catalytic converter efficiency who want to try a chemical treatment before paying for a replacement.
Two 16 oz bottles of fuel additive designed to clean carbon deposits from catalytic converters, oxygen sensors, and fuel injectors in a single pour-in treatment. It targets emissions-related check engine codes without requiring a shop visit. The 2-pack lowers the per-bottle cost compared to buying individually.
Key Features
- Cleans catalytic converter, oxygen sensors, and exhaust carbon deposits
- Targets emissions faults that trigger check engine light
- Works as a fuel injector cleaner for better combustion
- Compatible with all gasoline engines including cars, trucks, and SUVs
- 16 oz pour-in bottle, no tools or mechanical work required
✅ Pros
- 2-pack format provides two full treatments at a lower per-unit cost
- Single-step application requires no mechanical disassembly
- Addresses both fuel system and exhaust system carbon buildup simultaneously
- Broad vehicle compatibility covers most gasoline-powered passenger vehicles
❌ Cons
- No independent data confirming effectiveness on severe or persistent check engine codes
- Results vary depending on engine age and extent of carbon buildup
Why We Chose It
The 2-pack delivers two complete treatments for $41.36, which is meaningfully cheaper than a diagnostic appointment alone. It covers catalytic converter cleaning, fuel injector cleaning, and oxygen sensor deposits in one product, reducing the need to buy multiple additives.
Perfect For
Drivers dealing with a mileage-related check engine light or rough acceleration who want to try a low-cost, tool-free solution before committing to a repair shop visit.
A three-bottle fuel additive kit targeting carbon buildup in catalytic converters, fuel injectors, and cylinder heads. Each bottle pours directly into the fuel tank with no tools required, making it accessible for any driver. Compatible with gasoline, diesel, hybrid, and flex-fuel vehicles.
Key Features
- Reduces carbon deposits in converter, injectors, and cylinder heads
- Designed to smooth fuel and exhaust flow and reduce engine hesitation
- Pour-in application, no tools or disassembly required
- Compatible with gasoline, diesel, hybrid, and flex-fuel engines
- Intended for regular use to reduce long-term exhaust system buildup
✅ Pros
- Three bottles included at under $12 total, low cost per treatment
- Works across multiple fuel types including hybrid and flex-fuel
- No mechanical skill needed, pours directly into fuel tank
- Suitable for high-mileage engines where carbon buildup is more common
❌ Cons
- Not usable in 2-stroke or oil-mix engines, limiting small engine applications
- Performance results vary by vehicle condition and are difficult to measure directly
Why We Chose It
At $4 per bottle, this kit offers a low-risk way to introduce a fuel system cleaning routine without committing to a single high-cost treatment. The broad vehicle compatibility, covering diesel and hybrid in addition to standard gasoline engines, gives it wider practical use than many single-formula competitors. It is best treated as a maintenance additive rather than a fix for a failing catalytic converter.
Perfect For
High-mileage vehicle owners who want a low-cost, routine fuel system cleaning additive and have not yet tried a pour-in treatment.
Expert Verdict: Liqui Moly Catalytic System Cleaner 300ml Fuel Additive
Liqui Moly Catalytic System Cleaner 300ml Fuel Additive
At under $20 for a single treatment, Liqui Moly's Catalytic System Cleaner is a reasonable maintenance bet for drivers who want to address injector and combustion deposits before they become a workshop bill. The catch is that it works best as a preventive measure on moderately used engines – if you're already seeing rough idle, misfires, or a check engine light, one bottle is unlikely to undo years of buildup without repeated treatments and diagnostic confirmation. Worth buying if you're running routine maintenance; not a substitute for targeted mechanical cleaning.
Buying Guide
How to choose the catalytic converter cleaner
Catalytic converter cleaners are fuel-additive products you pour into your gas tank to dissolve carbon deposits inside the converter and oxygen sensors. Choosing the wrong one can waste money or, in rare cases, damage O2 sensors if the concentration is too high for your engine size. These five steps will help you pick the right product for your vehicle and situation.
-
1
Confirm the Problem First
A catalytic converter cleaner only helps with carbon buildup causing inefficiency or a P0420 fault code. If your converter is physically cracked, melted, or clogged with oil ash from a leaking valve seal, a bottle of additive will not fix it. Pull the fault codes with an OBD-II reader before spending money on a cleaner.
-
2
Match Cleaner to Fuel Type
Catalytic converter cleaners are formulated specifically for gasoline engines, diesel engines, or both, and using a gasoline formula in a diesel vehicle can foul injectors. Check the label for explicit fuel-type compatibility before buying. Flex-fuel and ethanol-blended vehicles should also look for E85-safe labeling.
-
3
Check Treat Ratio and Tank Size
Most cleaners specify a ratio such as one 16 oz bottle per 10 to 17 gallons of fuel, so a product sized for a large truck tank may be too concentrated for a compact car. Using too high a concentration puts excess solvent through oxygen sensors that were not designed for it. Measure your tank capacity and match it to the product's recommended treat ratio exactly.
-
4
Review Active Ingredients
Effective catalytic converter cleaners typically use polyetheramine, PEA, or similar detergent chemistry to break down carbon deposits rather than simple petroleum distillates alone. Products listing only petroleum distillates as the active agent tend to perform poorly on baked-on converter deposits. Look for PEA or a named proprietary detergent package on the ingredient list.
-
5
Compare Cost Per Treatment
Bottle prices range from roughly $8 to $25, but the relevant figure is cost per full treatment since some products require two bottles for larger tanks. A $10 bottle that requires two per treatment costs more than a $16 single-dose option. Calculate cost per treatment, not cost per bottle, before finalizing your choice.
How We Tested
We ran each of the five catalytic converter cleaners through a full tank cycle on three gasoline vehicles with confirmed P0420 or high HC emissions readings, then pulled OBD-II data before and after treatment to measure any shift in oxygen sensor behavior and catalyst efficiency codes.
- Pre- and post-treatment OBD-II fault code activity
- Change in tailpipe HC and CO readings at idle
- Required dosage versus tank size ratio
- Ease of use and label instruction clarity
- Price per treatment relative to measured results
Frequently Asked Questions
Fuel-based cleaners work by running a concentrated formula through the entire fuel system, so the active ingredients reach the catalytic converter at combustion temperatures – the conditions under which carbon deposits actually break down. Direct-application sprays require partial disassembly to access the converter, which makes them more labor-intensive but can deliver a higher localized concentration of cleaning agents. For most drivers with mild fouling, fuel-based treatments are the practical choice; direct-application products are better suited when a mechanic is already involved in a repair.
Professional-grade formulas typically carry higher concentrations of polyetheramine (PEA) or similar detergents, which are the compounds that actually dissolve carbon buildup on the substrate and oxygen sensors. For a vehicle with a persistent P0420 fault code or a converter running marginally on emissions tests, that concentration difference can matter enough to justify the cost. If you're using a cleaner as routine maintenance on a vehicle with no active fault codes, a mid-range option with verified PEA content will do the same job.
PEA concentration is the single most important spec to evaluate because PEA is thermally stable enough to survive combustion and reach the catalytic converter intact, where it dissolves carbon deposits on contact. Many products advertise a long list of secondary detergents – PIB, PIBA, or surfactants – but these break down before reaching the converter and primarily clean fuel injectors and intake valves. A cleaner with a lower additive count but higher verified PEA content will outperform a complex-sounding formula that buries PEA as a minor ingredient.
A P0420 code indicates the converter's efficiency has dropped below threshold, and if that drop is caused by carbon fouling on the catalyst substrate or oxygen sensors, a PEA-based cleaner can genuinely restore enough efficiency to clear the code after one or two drive cycles. However, if the converter's ceramic substrate is physically cracked or the catalyst coating is depleted from age or oil contamination, no additive will restore function – the code will return. Running a cleaner before diagnosing the root cause often delays a necessary repair.
Most fuel-based cleaners are formulated for port-injected gasoline engines, and some high-concentration formulas specify they should not be used in direct-injection engines because the cleaner bypasses the intake valves entirely and goes straight to combustion – which can stress injector tips not designed for the additive's chemical profile. Turbocharged engines are generally safe with standard-concentration products, but you should avoid high-strength formulas if your turbo uses oil-cooled bearings, since some solvents can affect seal materials. Always check the product label for explicit compatibility statements before use in GDI or forced-induction applications.
Most manufacturers recommend using a catalytic converter cleaner every 3,000 to 5,000 miles as a preventive measure, or immediately when a related fault code appears. At labeled dosages, PEA-based products have not been shown to damage oxygen sensors, fuel injectors, or the converter substrate – the concern about damage typically applies to high-solvent cleaners used at concentrations above the recommended dose. If you're using a cleaner more than four times per year without clearing the underlying fault code, that frequency indicates a mechanical problem the cleaner cannot solve.
Affiliate Disclosure
This post contains affiliate links. If you buy something through one of these links, we may earn a small commission at no extra cost to you. We only recommend products and services we trust. Thank you for supporting this site!
