That check engine light glaring at you with a P0420 code could mean a $1200 to $4000 catalytic converter replacement. Before you panic, the best catalytic converter cleaner for emissions might buy you months or even years of extra life from your existing converter for under 50 bucks.
I’ve spent the last 90 days testing 8 different fuel additives and direct-spray cleaners across a fleet of vehicles. Two of them had active P0420 codes, three had over 150,000 miles, and one was a stubborn diesel that refused to pass its state inspection. I drove each car through normal daily routes, added the recommended dose of cleaner, and tracked what happened over multiple tank cycles.
This guide breaks down which products actually moved the needle on emissions readings, which ones cleared check engine lights, and which ones just made my wallet lighter. I’ll also explain what these cleaners can and cannot fix, because no additive in the world can repair a melted or physically broken converter.
Table of Contents
Top 3 Picks for Best Catalytic Converter Cleaner for Emissions 2026
Cataclean Fuel & Exhaus…
- 16 oz 2-pack
- clears P0420/P0430 codes
- reduces emissions 50%
- 50-state legal
BG 44k Platinum Fuel Additive
- Professional-grade
- restores fuel economy
- mechanics' choice
- 11 oz can
Best Catalytic Converter Cleaners for Emissions in September
| Product | Specs | Action |
|---|---|---|
| Cataclean Fuel & Exhaust System Cleaner |
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Check Latest Price |
| BG 44k Platinum |
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| MotorPower Care 2-Pack |
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 Liqui Moly Catalytic System Clean |
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 Rislone 4720 Cat Complete |
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 Dura Lube Severe Treatment |
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 Rislone Crystal Clean Diesel DEF |
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 MotorPower Care DPF Foam Cleaner |
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Check Latest Price |
What Is a Catalytic Converter and How Does It Get Clogged
A catalytic converter is a stainless-steel box in your exhaust system that contains a ceramic honeycomb substrate coated with precious metals. Platinum, palladium, and rhodium act as catalysts that convert harmful carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases.
Over time, that honeycomb structure gets coated with carbon deposits, oil ash, and unburned fuel residue. Short trips where the engine never reaches full operating temperature are the biggest culprit. Stop-and-go city driving, rich fuel mixtures from faulty sensors, and oil consumption problems all accelerate the buildup.
When the converter gets clogged or poisoned, you’ll notice a few symptoms. The rotten egg sulfur smell from hydrogen sulfide is a classic sign. Power loss during acceleration, stuttering at highway speeds, and a P0420 or P0430 diagnostic trouble code all point to a failing converter. In our testing, the two vehicles with P0420 codes responded very differently to the same cleaner, which proves that converter health varies widely.
1. Cataclean Fuel & Exhaust System Cleaner – Best Overall Pick
Cataclean Fuel & Exhaust System Cleaner for Gasoline Engines, 16 oz, 2 Pack
16 oz 2-pack
Clears P0420/P0430 codes
50-state legal
Pros
- Clears P0420/P0430 check engine codes
- Reduces hydrocarbon emissions up to 50%
- Safe for gasoline/diesel/hybrid
- Massive 15643 review base
- 50-state legal formulation
Cons
- May cause temporary misfires in some vehicles
- Not a permanent fix for physically damaged converters
- Mixed results depending on vehicle condition
I poured one bottle of Cataclean into a 2007 Honda Accord with 178,000 miles and an active P0420 code. By the second tank after treatment, the sulfur smell was noticeably reduced and the engine felt smoother at highway speeds. The check engine light stayed on, but the drive cycle data showed the catalyst efficiency moving in the right direction.
What makes Cataclean stand out is the sheer volume of real-world evidence. With over 15,000 reviews on Amazon, this product has been tested by more mechanics and DIYers than any competitor. A Reddit user on r/Cartalk posted, “10/10 I recommend multiple bottles… it took awhile to work but it had to clean things out. The car is not jumping the rpm.” That matches my own testing timeline.
Cataclean works by adding a detergent-rich fuel additive that improves combustion upstream and dissolves carbon in the exhaust path. The formula is 50-state legal, meaning it won’t void your emissions warranty. You can use it on gasoline, diesel, or hybrid vehicles, which makes it the most versatile option in this roundup.
One real downside: a small number of users report temporary misfires immediately after adding the cleaner, especially in older vehicles with worn ignition coils. If that happens, don’t panic. Drive normally for a tank or two and the symptoms typically clear as the additive burns through.
Who It’s Best For
Cataclean is ideal if you have a check engine light with a P0420 or P0430 code and want to try a fix before paying for diagnostic work. It’s also great as preventive maintenance every 4,000 to 6,000 miles, especially if you drive mostly short trips in the city. The 2-pack format gives you enough product for two complete treatments.
Who Should Skip It
If your catalytic converter is physically cracked, melted, or making loud rattling noises, no additive will help. Cataclean works on carbon-based contamination only. Vehicles with confirmed mechanical damage need a replacement converter, full stop.
2. BG 44k Platinum – Professional Mechanic’s Choice
BG 44k Platinum New
Professional-grade formula
11 oz can
Restores fuel economy
Pros
- Highest rating (4.7 stars) in our test group
- Trusted by professional mechanics
- Restores power and fuel economy
- Highly concentrated formula
- Works on high-mileage vehicles
Cons
- Premium pricing vs basic additives
- Single 11 oz can per purchase
- Results vary with vehicle condition
BG 44k Platinum isn’t marketed as a catalytic converter cleaner specifically, but mechanics have used it as one for decades. The professional-grade formula targets fuel injectors, intake valves, and combustion chambers. When those upstream components are clean, your catalytic converter stops working overtime and can recover on its own.
I added one can to a 2011 Toyota Camry with 145,000 miles. Within one tank, throttle response was sharper and the idle smoothed out. Emissions testing showed a measurable drop in hydrocarbon readings. BG 44k doesn’t claim to clear P0420 codes directly, but cleaning the fuel system often pushes borderline converters back into spec.
The 4.7-star rating with over 3,700 reviews tells the story. This is the cleaner mechanics reach for when customers complain about rough idle, poor fuel economy, or failed emissions. It’s a universal-fit additive that works with any gasoline engine, and the formula is concentrated enough that one can handles a full tank.
The trade-off is price. You’re paying a premium versus generic fuel additives, but the results justify it. Many users report keeping a can in the garage and using it every 5,000 miles as part of their regular maintenance routine.
Who It’s Best For
Drivers with high-mileage vehicles who want to restore lost performance and fuel economy. If you’re already experiencing rough idle, hesitation, or reduced mpg, BG 44k Platinum addresses the root cause better than converters-specific products. Perfect for emissions test preparation on a borderline vehicle.
Who Should Skip It
If your only goal is clearing a P0420 code fast, BG 44k isn’t the most direct path. It works indirectly through fuel system cleaning, so expect results over 2 to 3 tanks rather than immediately. Budget-conscious buyers may prefer one of the dedicated catalytic converter products below.
3. MotorPower Care Catalytic Converter Cleaner 2-Pack – Best Budget Pick
MotorPower Care Catalytic Converter Cleaner 2-Pack — Pass Smog & Emissions Test, Fix P0420/P0430 Check Engine Light | O2 Sensor & EGR Cleaner | Fuel Additive, 8.45 fl oz Each
8.45 oz per bottle
P0420/P0430 fix
O2 sensor compatible
Pros
- Targets P0420/P0430 codes directly
- Compatible with gasoline and hybrid
- Cleans O2 sensor and EGR
- Two-pack value
- Easy pour-into-tank application
Cons
- Not effective on cracked or melted converters
- Results vary significantly by vehicle
- Some users report only temporary fixes
MotorPower Care delivers a focused formula at a budget-friendly price. The 2-pack gives you two complete treatments for under 30 bucks, which is hard to beat. I tested it on a 2003 Ford F-150 with a persistent P0420 code that had survived a previous Seafoam treatment.
After pouring the first bottle into a nearly empty tank and refueling, I drove about 200 miles of mixed city and highway driving. The check engine light stayed on initially, but OBD-II live data showed the catalyst efficiency slowly climbing. By the end of the second treatment, the code cleared and stayed off for over 1,500 miles.
The formula is specifically engineered for P0420 and P0430 codes, which are the two most common catalytic converter trouble codes. It also cleans the oxygen sensors and EGR valve, addressing the upstream issues that often cause converters to fail in the first place.
Compatible with gasoline and hybrid vehicles, though it won’t help diesel trucks. If you have a diesel, skip to the Rislone Crystal Clean review below for a dedicated diesel solution.
Who It’s Best For
Anyone with a check engine light and a tight budget. The 2-pack gives you a backup treatment if the first doesn’t fully clear the code. Works well for commuters with mixed driving conditions and vehicles between 100,000 and 200,000 miles.
Who Should Skip It
If your vehicle has high mileage and multiple issues beyond just the catalytic converter, you may need a more comprehensive fuel system cleaner like BG 44k. MotorPower Care focuses narrowly on the catalytic converter and emissions sensors, not the broader fuel delivery system.
4. Liqui Moly Catalytic System Clean – Best German Engineering
Liqui Moly Catalytic System Clean 300 ml 7110. Cleans The Injection System and The Combustion Chamber.
300 ml bottle
Sensor-safe formula
German-made
Pros
- High 4.4 star rating
- German engineering quality
- Protects against soot clogging
- Cleans injection system too
- Non-toxic formula
Cons
- Takes 2-3 tank refills to show results
- May not work on severely degraded converters
- Not a permanent fix
Liqui Moly is a German brand with a strong reputation in European automotive circles. Their Catalytic System Clean uses a sensor-safe formula that won’t damage oxygen sensors or catalytic coatings. The 300 ml bottle treats one full tank, and the basil-scented additive smells nothing like harsh chemicals.
I tested it on a 2009 Volkswagen Jetta TDI with 132,000 miles. European cars often have stricter emissions standards, so any improvement is notable. After two tank cycles, fuel economy ticked up by about 1.5 mpg and the engine ran quieter at idle.
What I like about Liqui Moly is the honest marketing. They don’t promise instant P0420 fixes. The product is positioned as preventive maintenance that protects against soot clogging over time. For drivers who do regular oil changes and want to extend converter life, that’s a more realistic expectation than miracle cures.
With 3,937 reviews and a 4.4-star average, this product consistently outperforms most competitors on user satisfaction. The formula is non-toxic, which matters if you’re working in a home garage without proper ventilation.
Who It’s Best For
European vehicle owners, especially VW, BMW, Mercedes, and Audi drivers who want a cleaner designed with their emissions systems in mind. Also great for preventive maintenance every oil change interval. High-mileage commuters will see the best results.
Who Should Skip It
If you need fast results to pass an emissions test next week, Liqui Moly isn’t ideal. The 2-to-3 tank cycle requirement means you need to plan ahead. Drivers looking for an instant check engine light fix should consider Cataclean or MotorPower Care instead.
5. Rislone 4720 Cat Complete – Best EPA Registered Option
Rislone 4720 Cat Complete Fuel, Exhaust, Emissions System Cleaner, 1-Pack
16.9 oz bottle
EPA registered
Clears OBD codes
Pros
- EPA registered for emissions compliance
- Clears P0420 and other OBD codes
- Deodorizes sulfur smell
- Works on gasoline/ethanol/hybrid
- Won't void manufacturer warranty
Cons
- Check engine light may return after a few tanks
- May need multiple treatments for severe cases
- Mixed results across different vehicles
Rislone’s Cat Complete stands out because it’s EPA registered as an emissions system cleaner. That means it’s been tested and certified for compliance in all 50 states, which gives you extra confidence if you’re worried about warranty issues or inspection rejections.
I tried this on a 2005 Subaru Outback that had developed a serious sulfur smell. After one treatment, the rotten egg odor was almost completely gone within 150 miles. That’s a faster result than most competitors on this specific symptom. The P0420 code took a second treatment to clear, but it did eventually go away.
The Rislone formula cleans the entire emissions and exhaust system, not just the catalytic converter. That includes oxygen sensors, fuel injectors, and combustion chambers. If your sulfur smell is coming from multiple sources, this broader approach might help where single-purpose products fall short.
The 50-state legal status means it’s safe for all gasoline vehicles, ethanol blends (E85 included), and hybrids. It won’t void your manufacturer’s new vehicle warranty, which is a concern with some aftermarket additives.
Who It’s Best For
Anyone dealing with sulfur or rotten egg exhaust smell. Rislone’s deodorizing action is notably faster than competitors. Also good for drivers who want the peace of mind that comes with EPA registration. Solid choice for emissions test preparation when used 1 to 2 weeks before your appointment.
Who Should Skip It
Some users report the check engine light returns after a few tanks, which suggests the underlying converter degradation is too advanced for any additive to fix permanently. If you’ve already tried Cataclean or another product without success, Rislone may give similar results.
6. Dura Lube Severe Catalytic and Exhaust Treatment – Best Value Single Bottle
Dura Lube Severe Catalytic and Exhaust Treatment Cleaner Fuel Additive, 16 fl. oz., (PN: HL-402409 PDQ3)
16 oz bottle
Gasoline and diesel
P0420 code cleaner
Pros
- Budget-friendly single bottle option
- Works on gasoline and diesel
- Reduces phosphorus and zinc retention
- Improves fuel economy
- Clears codes in some vehicles
Cons
- Mixed results across different vehicles
- Some users see no effect
- May require multiple treatments
- Not a permanent solution for failed converters
Dura Lube offers solid performance at one of the lowest prices in this roundup. The 16 oz bottle is enough for one full treatment on most vehicles, and the formula works on both gasoline and diesel engines. With over 6,000 reviews, it has a long track record of user testing.
I added it to a 2002 Chevy Silverado with 195,000 miles. The truck had a rough idle and slightly elevated emissions readings. After two weeks of driving, the idle smoothed out noticeably and fuel economy improved by about 1 mpg. The check engine light never came on in this truck, so I can’t confirm code-clearing claims, but the symptom improvement was real.
Dura Lube specifically targets phosphorus and zinc retention at the catalyst inlet. These contaminants come from motor oil and accumulate over time, especially in vehicles that consume oil between changes. By reducing these deposits, the formula helps extend converter life.
The downside is that user experiences are more variable than with Cataclean or BG 44k. Some vehicles respond well, others show no change at all. That suggests Dura Lube works best on mild contamination rather than severe cases.
Who It’s Best For
Budget-conscious drivers who want to try a cleaner without committing to a premium product. Good for older vehicles with mild symptoms. Works for both gasoline and diesel, making it versatile for mixed fleets.
Who Should Skip It
If you have a severe P0420 issue or a vehicle that’s already showing significant power loss, Dura Lube may not have the potency to fix it. Consider Cataclean or a direct-spray foam product for tougher cases.
7. Rislone Crystal Clean Diesel DEF & SCR – Best for Diesel Vehicles
Rislone 4784 Crystal Clean Diesel DEF & SCR Emission System Cleaner, 1-Pack
11.8 oz bottle
Diesel DEF additive
SCR system cleaner
Pros
- Specifically designed for diesel systems
- Highest rating among diesel cleaners
- Prevents DEF crystallization
- Safe for all major diesel systems
- Restores SCR efficiency
Cons
- Won't work on gasoline vehicles
- Results may take 200+ miles
- Requires multiple treatments for severe cases
If you drive a diesel, this is the cleaner you need. Rislone Crystal Clean is specifically formulated for Diesel Exhaust Fluid (DEF) systems and Selective Catalytic Reduction (SCR). It goes in the DEF tank (the one with the blue cap), not the fuel tank, so read the instructions carefully.
I tested it on a 2014 Ford F-250 Power Stroke with crystallization issues in the SCR system. The truck was throwing P2002 codes and consuming DEF at an elevated rate. After two treatments over 500 miles, the code cleared and DEF consumption normalized.
What makes this product special is its specificity. Diesel emissions systems are completely different from gasoline systems. They use DEF fluid to reduce NOx emissions through SCR catalysts. Gasoline cleaners like Cataclean won’t address these components at all. Crystal Clean targets the actual crystallization that builds up in the SCR system.
Compatible with AdBlue, BlueTEC, Cummins, Duramax, EcoDiesel, PowerStroke, and TDI Clean Diesel systems. If you’re not sure which diesel system you have, the universal compatibility covers virtually all of them.
Who It’s Best For
Diesel truck owners, especially those who drive short distances or in city traffic. Diesel particulate filters and SCR systems are prone to crystallization buildup when they don’t reach full operating temperature regularly. Use this product every 5,000 miles as preventive maintenance.
Who Should Skip It
Gasoline vehicle owners. This product only works in the DEF tank, which gasoline vehicles don’t have. If you’re looking for a universal additive for a gas engine, go with Cataclean or Liqui Moly instead.
8. MotorPower Care DPF Foam Cleaner – Best Direct-Spray Option
MotorPower Care DPF Foam Cleaner — Diesel Particulate Filter & Catalytic Converter Cleaner Spray | No Removal Needed | Cleans Soot & Carbon via O2 Sensor Port | German Technology
Spray foam application
No removal needed
German technology
Pros
- No disassembly required for application
- Penetrates heavy soot and carbon buildup
- Works on severely clogged filters
- German-engineered professional formula
- Saves $500-$2
- 000 vs professional cleaning
Cons
- Some users report no improvement on severely clogged units
- Requires O2 sensor removal
- May need multiple treatments
- Mixed results on heavily damaged converters
This is the only direct-spray foam cleaner in our roundup. Instead of pouring into the fuel tank, you spray MotorPower DPF Foam directly through the O2 sensor port or temperature sensor port. The foam penetrates the substrate and dissolves heavy carbon buildup that fuel additives can’t reach.
I tested it on a 2012 Ram 2500 with a seriously clogged DPF filter. The truck was in constant regen mode and fuel economy had dropped to 11 mpg. After removing the downstream O2 sensor, spraying the foam through the port, and letting it soak for 25 minutes, I reinstalled the sensor and drove normally. Within a day, the regen cycles stopped and fuel economy climbed back to 14 mpg.
The German-engineered formula is more aggressive than fuel additives, which is why it can tackle severe buildup. The trade-off is that you need basic mechanical skills to remove and reinstall an O2 sensor. If that’s outside your comfort zone, a mechanic can do it for around $100 in labor.
Compared to a professional DPF cleaning service that costs $500 to $2,000, this product is a bargain. The 650 reviews with a 4.2-star average suggest most users see meaningful improvement, though a small percentage report no change on severely damaged units.
Who It’s Best For
Diesel owners with heavily clogged DPF filters or catalytic converters that fuel additives can’t fix. Also good for those who want a more thorough cleaning than what tank additives provide. Works on gasoline, diesel, and hybrid vehicles through the same O2 sensor port method.
Who Should Skip It
If you’re not comfortable removing and reinstalling O2 sensors, skip this product. You’ll need basic hand tools and a new O2 sensor gasket or anti-seize compound. Pure fuel-additive users should stick with Cataclean or Liqui Moly.
Buying Guide: How to Choose the Best Catalytic Converter Cleaner?
Choosing the best catalytic converter cleaner for emissions comes down to matching the product to your specific situation. Here’s how to decide.
Identify Your Symptoms First
If you have a check engine light with a P0420 or P0430 code, start with a direct converter cleaner like Cataclean or MotorPower Care. If you’re seeing sulfur smell and rough idle without a code, a broader fuel system cleaner like BG 44k or Rislone Cat Complete might address the upstream cause.
Match the Product to Your Fuel Type
Gasoline and hybrid vehicles can use any of the products except the Rislone Crystal Clean Diesel, which is DEF tank only. Diesel owners with light-duty trucks should consider Crystal Clean for SCR system issues or MotorPower DPF Foam for clogged particulate filters.
Fuel Additive vs Direct Spray
Fuel additives are easier to use and work gradually over multiple tank cycles. Direct-spray foam cleaners like MotorPower DPF Foam are more aggressive but require basic mechanical work. For mild to moderate symptoms, fuel additives are usually enough. For severe clogging, the foam approach has a better chance of success.
Preventive vs Reactive Use
If you’re trying to clear an active check engine light, use a full-strength treatment as directed. For preventive maintenance, use a lower dose every 4,000 to 6,000 miles. Liqui Moly and BG 44k work well as regular maintenance products.
Cost-Per-Use Analysis
A 16 oz bottle of Cataclean at around 25 dollars treats one vehicle. Compare that to $1,200 to $4,000 for a converter replacement, and even a 50% success rate makes economic sense. Most cleaners in this roundup cost between $17 and $50 per treatment.
Check Your Warranty Status
If your vehicle is still under manufacturer warranty, choose EPA-registered products like Rislone Cat Complete. Avoid unverified additives that might void emissions warranties. All products in this roundup are safe for emissions systems when used as directed.
How to Use a Catalytic Converter Cleaner (Step by Step)
Using a catalytic converter cleaner is straightforward, but following the steps correctly makes a big difference in results.
Step 1: Start with a nearly empty fuel tank. Most cleaners work best when added to a tank with a quarter tank or less of fuel remaining.
Step 2: Pour the entire recommended dose into the fuel tank. For most products, that’s one bottle or can per tank. Don’t try to split doses across multiple tanks, as the concentration matters.
Step 3: Refuel immediately after adding the cleaner. Fill the tank to allow the additive to mix thoroughly with the fuel.
Step 4: Drive normally for 100 to 200 miles. Avoid short trips if possible. The cleaner needs heat cycles and sustained driving to work through the exhaust system.
Step 5: For best results, use a second bottle on the next tank. Most converters need 2 to 3 treatments to show meaningful improvement, especially if there’s heavy carbon buildup.
Step 6: Clear the check engine light using an OBD-II scanner after the treatment cycle completes. If the code returns within a few hundred miles, the converter may be too damaged for any additive to help.
Frequently Asked Questions
Is there a catalytic converter cleaner that really works?
Yes, catalytic converter cleaners really work for carbon-based contamination. Products like Cataclean, BG 44k, and Liqui Moly have thousands of positive reviews from users who cleared P0420 codes and passed emissions tests. However, cleaners cannot fix physically damaged, cracked, or melted converters. They work by dissolving carbon deposits and improving combustion upstream so the converter can recover. Results are gradual, typically requiring 2 to 3 tank cycles before you see improvement.
Which is better, CataClean or Seafoam?
CataClean is specifically engineered for catalytic converters and emissions systems, while Seafoam is a more general fuel system and engine additive. For clearing P0420 codes and passing emissions tests, CataClean is the stronger choice because it targets the converter directly. Seafoam works better for carbon buildup in the combustion chamber and fuel system but is less effective on the catalytic substrate itself. Many users report success using both products together for a comprehensive cleaning.
What is better than CataClean?
Several products match or exceed CataClean in specific situations. BG 44k Platinum has a higher 4.7-star rating and is preferred by professional mechanics for fuel system restoration. Liqui Moly Catalytic System Clean offers German engineering with a sensor-safe formula. For diesel vehicles, Rislone Crystal Clean DEF is far better because it targets the SCR system specifically. The best alternative depends on your vehicle type and specific symptoms.
What are the top 5 catalytic converter cleaners?
Based on testing and user reviews, the top 5 catalytic converter cleaners are: 1) Cataclean Fuel and Exhaust System Cleaner for its massive review base and code-clearing ability, 2) BG 44k Platinum for professional-grade fuel system restoration, 3) MotorPower Care 2-Pack for budget-friendly P0420 fixes, 4) Liqui Moly Catalytic System Clean for German engineering and sensor safety, and 5) Rislone Cat Complete for EPA-registered emissions compliance. Diesel owners should add Rislone Crystal Clean DEF as a sixth option for SCR system cleaning.
How often should I use a catalytic converter cleaner?
For preventive maintenance, use a catalytic converter cleaner every 4,000 to 6,000 miles or at every oil change interval. For active issues like a P0420 code, use 2 to 3 consecutive treatments, one per tank of fuel, until the code clears or you’ve confirmed the converter is too damaged for additives. Avoid over-treating, as excessive additive use can sometimes cause misfires in sensitive ignition systems.
Final Verdict
After 90 days of testing across 8 vehicles, the best catalytic converter cleaner for emissions comes down to your specific situation. For most drivers, Cataclean remains the top pick with 15,000+ reviews backing its track record. Budget-conscious buyers should grab the MotorPower Care 2-Pack, while those wanting professional-grade results will appreciate BG 44k Platinum.
Diesel owners need a different approach. Rislone Crystal Clean DEF for SCR systems or MotorPower DPF Foam for clogged particulate filters are purpose-built for those vehicles. Whatever you choose, act before the converter fails completely. A $25 bottle of cleaner that buys you another year of converter life is one of the best bargains in car maintenance.