Converter Basics: Installing a new converter

A catalytic converter has three main components:

  • The converter body, which includes the “can,” pipes, and matting used to hold the brick in place.
  • The converter substrate – usually a high performance ceramic “brick,” engineered with thousand of tiny channels through which the exhaust gases pass. The substrate can also be constructed of a metal mesh.
  • The washcoat, which coats the substrate with a combination of precious metals; platinum, palladium, and / or rhodium.

In addition to these components, many converters will have O2 sensor ports and air tubes.

How a catalytic converter works

As exhaust gases pass into the converter and through the substrate, the washcoat creates chemical reactions that lower the level of emissions emitted from the tailpipe.

A catalytic converter needs two factors to operate properly: suffi cient operating temperature (the “light off” temperature) and a steady stream of feed gas. Once the “light off” temperature is reached the catalytic conversions occur: 1) oxides of nitrogen (NOx) are reduced into nitrogen and carbon dioxide, and 2) hydrocarbons (HC) and carbon monoxide (CO) are oxidized to create water vapor.

Converters typically start to work at around 550ºF. The majority of the purifi cation takes place once the converter reaches at least 750ºF.

Diagnosing catalytic converter failures

When a converter malfunctions, it can be due to an engine performance issue or an issue with any of the components in the fuel, engine, and exhaust systems. Typical issues include faulty O2 sensors, incorrect air/fuel ratio, unburned fuel entering the unit, chemical additives in the fuel, malfunctioning sensors, ECM failure, and road damage. One or more of these conditions can trigger a change in emissions at the converter, causing the ECM to record a code that indicates “Catalyst Efficiency Below Threshold”.

If a catalytic converter has failed, it is up to the technician to thoroughly diagnose the problem to fi nd out what caused the failure. If this is not done, it will eventually lead to failure of the new converter.

Codes PO420 and PO430 indicate that the “catalyst system efficiency is below threshold bank 1 or 2. In other words, the vehicle’s oxygen sensors downstream noticed that the converter is not working as efficiently as it should be. However, code PO420 and PO430 can occur for a variety of reasons other than converter failure or malfunction. It is important to properly diagnose and identify any problem or problems before installing a new catalytic converter. 

Converter replacement requires ECM reset

When a converter is replaced, the technician will need to perform a drive cycle in order to correctly reset the ECM. Follow the manufacturer guidelines for the correct drive cycle.

Conditions that can lead to a Code PO420 and PO430:

Fuel trim too high

  • Vacuum leaks
  • Intake leaks
  • Bad mass-air flow sensor

Fuel trim too low

  • Stuck fuel injectors
  • Bad fuel pressure regulator

O2 sensor problems

  • Failed or “lazy” sensor
  • Sensor contamination by antifreeze, additives, oil, unburned fuel, or service chemicals/sealants

Maintenance / operation problems

  • Overloaded vehicle
  • Incorrect engine timing
  • Carbon deposits

Mechanical / electrical issues

  • ECM failure
  • Defective electrical parts:
    plugs, wires, coils
  • Improper compression
  • Leaking valves
  • EGR failure
  • Exhaust leaks
  • Worn camshaft
  • Transmission problems
  • Improper fuel system performance
  • Blown head, intake, or exhaust gaskets
  • Bad valve timing
  • Cooling system issues