Subaru WRX STI Catalytic Converters Guide

Subaru WRX STI Catalytic Converters: The Subaru WRX STI is a high-performance sedan known for its rally-inspired design. From 2004 onwards, all WRX STI models were powered by a turbocharged 4-cylinder engine and featured multiple catalytic converters for enhanced exhaust gas purification. These catalytic converters are crucial in reducing harmful emissions and ensuring compliance with environmental regulations. With its powerful performance and advanced emission control system, the Subaru WRX STI offers an exhilarating driving experience and environmental responsibility.

Direct-fit replacement Subaru WRX STI Catalytic Converters are available from aftermarket brands like Autozone catalytic converter, Bosal, Eastern Catalytic, and Walker. Proper inlet/outlet dimensions and flange style must match the original converters. Subaru WRX STI Catalytic Converters sold in California must be CARB-compliant.

Specific Details on the Subaru WRX STI Catalytic Converters

Common Signs For Bad or Clogged Subaru WRX STI Catalytic Converters

  • Check engine light: Warning light for the engine. Checking the engine warning light is a valuable way to tell whether or not there is a problem with the emissions system in your vehicle. A professional mechanic must check out your car immediately if the “check engine” light turns on in your dashboard.
  • Reduced fuel economy: Your car’s fuel consumption efficiency may suffer if Subaru WRX STI Catalytic Converters malfunctions since it cannot convert dangerous exhaust gases into less harmful gases at the same efficiency level.
  • Engine Misfires: If Subaru WRX STI Catalytic Converters aren’t working properly, it could cause engine misfires. This is because the catalytic converter cannot reduce the quantity of carbon monoxide in the exhaust fumes.
  • Increased Emissions: A catalytic converter in your car that isn’t working properly may cause increased emissions. This is due to the inability of the catalytic converter to transform hazardous exhaust gases into gases that are less detrimental to the environment.
  • Excessive Exhaust Noise: Noise from the exhaust system that is excessive. A catalytic converter that is not working fine can create excessive noise from the exhaust system. This is due to the catalytic converter’s inability to significantly reduce the quantity of noise produced by the exhaust gases.
  • Dark Exhaust Smoke: An exhaust with a dark color is a symptom of a clogged catalytic converter, which can also generate this exhaust color. This is due to the inability of the catalytic converter to transform hazardous exhaust gases into gases that are less detrimental to the environment.

Troubleshooting Tips for Subaru WRX STI Catalytic Converters:

  • Check for P0420/P0430 codes pointing to converter failure using an OBD2 scanner.
  • Listen for rattling noises from the exhaust, indicating internal damage.
  • Inspect oxygen sensor performance upstream and downstream of converters.
  • Look for reduced performance, increased fuel usage, and rotten egg smells.
  • Use Catalytic Cleaner for catalytic converting cleaning

Installation Tips:

  • Always replace the exhaust inlet/outlet gaskets when installing the new Subaru WRX STI Catalytic Converters. High-temperature silicone sealant can also be used to seal connections.
  • The inlet/outlet pipe diameter is 2.5″. Ensure the replacement converters have the proper 2.5″ inlet and outlet ports.
  • When secured to the manifolds, use a torque wrench to tighten the converter mounting nuts/bolts to the proper spec of 22-27 ft-lbs.
  • Carefully detach and reattach the oxygen sensors from the original converters to the new ones in their same locations.
  • Clear any check engine codes with a scan tool after installing the new Subaru WRX STI Catalytic Converters. This will reset fuel trim parameters and monitor operation.

Read More: Subaru XV Crosstrek Catalytic Converters Ultimate Guide

Tips for Cleaning Subaru WRX STI Catalytic Converters:

  • Use a catalytic converter cleaner. Products like Catalytic Converter Cleaners can help break down and remove contaminants and deposits inside the catalytic converter. Follow the directions on the product.
  • Flush the catalytic converter. You can do this by adding the catalytic converter cleaner to your gas tank when filling up and then driving the car for 30-60 minutes on the highway. The high speeds and engine heat will help circulate the cleaner through the catalytic converter to remove deposits.
  • Use a shop vac to vacuum out loose debris. Disconnect the oxygen sensor and carefully insert the vacuum hose into the catalytic converter inlet. Be careful not to damage the honeycomb structure inside.
  • You may need to remove the catalytic converter and soak it in a solvent-based or acid-based cleaner for heavy carbon deposits. Make sure to thoroughly rinse and dry it before reinstalling.
  • Avoid using engine degreasers or harsh chemicals that could damage the catalyst material inside the converter. Stick to products specifically made for catalytic converter cleaning.
  • Be gentle in your cleaning methods to avoid damaging the converter. Over-cleaning or using too much pressure can harm the internal structure.
  • Consider having a professional mechanic do the cleaning if you’re uncomfortable with the process. They’ll have the proper tools and skills.

Read More: Subaru DL Catalytic Converters Ultimate Guide

Some Tips For Properly Washing Subaru WRX STI Catalytic Converters

  • Use a degreaser or catalytic converter cleaner. Spray it directly onto the exterior casing of the Catalytic Converters and let it soak for 5-10 minutes. This will help break down oil, grease, and carbon deposits. Avoid getting cleaner inside the converter.
  • Rinse the converter thoroughly with a garden hose or pressure washer. The high-pressure water will help blast away loosened contaminants.
  • Use a soft brush or rag to scrub the converter’s outside for stubborn deposits. Avoid abrasive pads or brushes that could damage the metal casing.
  • Ensure you thoroughly flush out any catalytic converter cleaner you use with plenty of water. Leftover chemical residue can damage the catalyst over time.
  • Dry the Subaru WRX STI Catalytic Converters fully after washing, using compressed air if available. Moisture left inside can also degrade the catalyst. Let the converter idle for 10-15 minutes to help evaporate any moisture.
  • Avoid using harsh chemicals like engine degreasers directly on the converter, as they can wash away the catalyst material and degrade performance over time.
  • Do not attempt to wash inside the converter or scrape at the honeycomb – this will destroy it. Only clean the outer casing.
  • Consider having a professional detail shop wash the catalytic converter if you don’t have the proper tools. They can properly clean it without damage.

The key is to be gentle and use only Catalytic Converter-approved cleaners. Thorough rinsing is important. Avoid excess moisture inside the converter.

Life Of Subaru WRX STI Catalytic Converters

  • Under normal driving conditions, the OEM Subaru WRX STI Catalytic Converters can average 120,000-150,000 miles.
  • The converters have an 8-year/80,000-mile federal emissions warranty. California emissions models have a 15-year/150,000-mile warranty.
  • Driving style has a big impact. Many short trips and cold starts can foul the converters faster than longer highway driving.
  • Poor engine maintenance, like oil leaks, bad spark plugs, or issues causing misfires, will degrade the converters quickly.
  • Contaminants like oil, coolant, or fuel getting into the exhaust can coat and damage the converter’s internals.
  • The upstream converter near the engine tends to fail sooner due to more heat cycling. The downstream one often lasts longer.
  • The efficiency declines if the Check Engine light comes on for a catalytic converter code. Replacement is recommended.
  • Periodic visual inspections of the converters can help spot potential issues early. Signs include blocked flow, rattling, and visible damage.
  • Aftermarket replacement converters typically have a shorter 50,000-80,000-mile lifespan. OEM parts tend to last longer.

How To Replace Subaru WRX STI Catalytic Converters


It uses multiple catalytic converters, one on each exhaust manifold bank. The new converters must be bolted into the original mounting positions for proper exhaust flow.

Exhaust Seals:

When installing the Subaru WRX STI Catalytic Converters, use new gaskets to seal the inlet and outlet flanges. Apply high-temperature silicone sealant as well to prevent leaks.

Oxygen Sensors:

Carefully detach and reattach the oxygen sensors from the old converters to the new ones. Position the upstream and downstream sensors properly.

Inspect Other Components:

Inspect the exhaust manifolds, mounts, and pipes when replacing the Subaru WRX STI Catalytic Converters. Look for any leaks or damage that needs addressing.

Post-Installation Check:

After installing the new Subaru WRX STI Catalytic Converters, clear any codes and road-test the vehicle. Verify the catalyst efficiency monitors are set to ready and that no check engine lights return.

FAQs Related to Subaru WRX STI Catalytic Converters

What Is A Catalytic Converter, And Why Is It Essential For My Subaru Wrx STI?

A catalytic converter is an emission control device that reduces harmful pollutants from your Subaru WRX STI’s exhaust. It plays a crucial role in reducing emissions to meet environmental standards.

How Is My Subaru Wrx STI’s Catalytic Converter Clogged Or Malfunctioning?

Look out for symptoms such as decreased engine performance, poor fuel economy, and warning lights on your dashboard. A diagnostic scan can also reveal any issues.

Can A Clogged Catalytic Converter Affect My Subaru WRX STI’s Engine Performance?

In extreme cases, a clogged catalytic converter can restrict exhaust flow, reducing engine power, fuel consumption, and even engine overheating.

What Is The Average Lifespan Of A Catalytic Converter In A Subaru Wrx STI?

The lifespan of a catalytic converter can vary. Still, generally, it can last anywhere from 100,000 to 150,000 miles or more if properly maintained.

What can I do to prolong the life of my Subaru WRX STI’s catalytic converter?

Regular maintenance, using high-quality fuel, and promptly addressing any engine issues can help extend your catalytic converter’s life.

How much does replacing a catalytic converter in a Subaru WRX STI cost?

The cost of replacement varies based on the converter’s type and your location. On average, it can range from $500 to $2,500, including parts and labor.

Can I Sell My Old Scrap Catalytic Converter From My Subaru WRX STI?

Yes, you can sell your old catalytic converter for scrap. These parts contain precious metals like platinum, palladium, and rhodium, which have value in recycling.

What Factors Determine The Scrap Price of a Subaru WRX STI Catalytic Converter?

The scrap price depends on the converter’s make, model, and the current market prices of precious metals. It can fluctuate over time.

Can I Clean a Clogged Catalytic Converter in My Subaru WRX STI, or Should I Replace it?

While catalytic converter cleaners are available, they are only sometimes effective for severely clogged converters. In such cases, replacement is often necessary.

What Is The Best Cleaner For Maintaining My Subaru Wrx STI’s Catalytic Converter?

Various catalytic converter cleaners are available, but following the manufacturer’s recommendations is essential. Consult your vehicle’s mechanic for specific product suggestions.

I am Nicolas, an automobile engineer with over 5 years of experience in exhaust systems and catalytic converters. I am passionate about learning and understanding how things work, and I am always looking for new ways to improve the performance and efficiency of automotive exhaust systems.

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