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What is a catalytic converter?

A catalytic converter is a mechanical device designed to convert the three most harmful elements present in a car’s exhaust into harmless elements. The three harmful elements being Hydrocarbons (unburned gasoline), Carbon Monoxide (accumulated by gasoline combustion), Nitrogen Oxides (formed when the nitrogen in the air is forced to combine with oxygen by the heat in the engine) A catalytic converter aids in converting carbon monoxide into carbon dioxide. It also helps in converting the hydrocarbons into water (H2O) and carbon dioxide. The nitrogen oxides are converted back into oxygen and nitrogen.  A catalytic converter has no moving parts and is designed to last the normal operating life of the vehicle.

Why did my catalytic converter fail?

Most catalytic Converters fail due to engine related problems. Replacing the catalytic converter without diagnosing and repairing the cause of the failure may lead to another ruined converter.

Potential causes for failed catalytic converters:

Overheated, melted, or broken converters
  • Misfires – Low compression, low spark, or no spark
  • Typically caused by an engine mechanical, ignition, or control system failure
Coated/Oil-Fouled Substrate
  • Excessive oil consumption (burning oil): bad rings or valve seals
  • Excessive carbon build-up in exhaust: Incorrect timing of fuel mixture, faulty spark plugs or plug wires, faulty check valve, oxygen sensors
  • Internal coolant leaks (head/intake gasket)
  • Improper fuels or additives: E85, diesel, sulfur (found in some low quality gasoline)
Structural Damage
  • Physical damage such as dents or cracks from road debris, collision, speed bumps, etc.
  • Metal fatigue / Stress fractures
  • Corrosion
  • Thermal shock: Cracked substrate that could occur from driving through a deep puddle

Miller CAT Universal Fit Catalytic Converters

  • All our Universal Catalytic Converters are engineered to be CARB legal and approved for use in California and all states that follow California Emission laws.
  • Built with T409 Stainless Steel to ensure longevity and strength.
  • CAD (Computer Aided Design) software is used to give our engineers the most efficient and innovative aftermarket catalytic converters. Each of our products were first designed in CAD, analysed for any inefficiencies, then spun formed to exact specifications to optimize air flow and maintain small form factor.
  • CNC Spin forming is used to ensure a seamless and compact design. Our compact designs are engineered to give the installer maximum maneuverability and ease of installation in limited spaces.

Miller CAT Direct Fit Catalytic Converters

  • All our Direct Fit Catalytic Converters are engineered to be CARB legal and approved for use in California and all states that follow California Emission laws.
  • Built using T409 Stainless Steel to ensure longevity and strength.
  • Engineered for an OE-style design and fit which includes OE hangers, flanges and bracket.
  • Vehicle application specific Jigs built from OE parts and CAD (Computer Aided Design) software helps ensure consistency and precision in production of our Direct Fit Catalytic Converters.

Identifying the right aftermarket Catalytic Converter for my vehicle

* It is illegal to install a catalytic converter based solely on physical shape, size, configuration, or pipe diameter *


1. Vehicle Manufacturer

2. Vehicle Model

3. Vehicle Year

4. Vehicle Specific Engine Size

5. Vehicle Test Group / Engine Family Number

6. Visit www.carbcats.com or California Air Resources Board Aftermarket Converter Database https://ssl.arb.ca.gov/AftermarketParts/catalysts to see which aftermarket part is approved to install.

7. If no EXACT match is found, then there are no aftermarket catalytic converters available at this time.


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