Skip Navigation

Select Language

Common Catalytic
Converter Q&A

Catalytic Converter FAQ

Getting answers

Have a catalytic converter question? Read on to get the answers to common catalytic questions.

Q: How do you determine what universal converter to use?

A: When installing a universal converter, it must still meet the emission requirements of the vehicle and cannot be chosen by size alone. By looking up a specific vehicle in the catalog or website, you will find the recommended universal converter with the appropriate loading. If a universal converter is not listed for your specific application, please refer to the universal converter specifications guidelines.   

Q: What makes a converter become red hot and/or melt the brick (thermal meltdown)?

A: Converters will get red hot when excess fuel is introduced directly into it, along with sufficient oxygen to burn the fuel. This is not a problem with the converter itself, but a result of a problem with the fuel system or ignition that allows unburned fuel to pass through the engine and then travel down into the converter. If the root cause is not corrected, the new converter will melt as well. 

Common causes of a melted converter are: 1) A three-way plus air vehicle is running rich, and when the air is injected into the converter, the rear brick will melt as the excessive fuel now has enough oxygen to burn inside the converter. 2) Vehicle is running rich with an exhaust leak, and when the air is drawn into the exhaust pipe and is combined with the excess fuel, it will burn in the converter. 3) The vehicle has a misfire. When the air-fuel charge leaves the combustion chamber without firing, it will travel through the exhaust pipe and burn in the converter.  

Q: What has caused my converter to become plugged (loss of power)?

A: If a converter is operated too long at a high temperature, the substrate may melt down and turn into a solid mass inside the converter. The vehicle may seem sluggish, as if there was a loss of power. Other causes might be: 1) Upstream converter has broken up and the debris has clogged a downstream unit. 2) The support mat may have become damaged and no longer retaining the brick in the correct position, allowing the brick to shift and block the exhaust flow.  

Q: What is chemical contamination of a converter (poisoning)?

A: If a replacement converter fails after a short period of time, then the root cause of the original failure has not been addressed. Some causes are contamination by silicone-based sealants; coolant leaks; oil blow by; and high sulfur fuel and/or rich fuel mixtures that form carbon deposits can quickly coat the substrate preventing it from working effectively.

Q: What is a three-way converter?

A: A three-way converter (also known as oxidation/reduction converters) is designed to control levels of carbon monoxide, hydrocarbons and oxides of nitrogen. Some three-way converters are equipped with an air injection tube, and this additional air (which comes from the air pump) assists the chemical reaction in the oxidation catalyst. Walker converters all utilize three-way catalyst technologies and operate in a two-way mode (controlling hydrocarbons and carbon monoxide) on older vehicles requiring a two-way converter.  

Q: How do I determine if I have a California emissions vehicle?

A: To determine if a vehicle has California emissions, check the emissions sticker on the vehicle, which is located in the engine compartment. If the sticker states the vehicle meets California requirements, CARB requirements, or 50-state, then the vehicle is equipped with California emissions. Click here for Engine Family Number information.

Q: Can I use a standard universal type converter on a vehicle with a diesel engine?

A: No. A diesel engine has different emissions requirements and a gas engine converter will not function on a diesel engine.

Q: Is there a physical difference between EPA-compliant exhaust systems and CARB-compliant exhaust systems?

A: Vehicles licensed outside of California, but built to California emissions standards, may have a physical difference from a vehicle built to Federal emissions standards. (If your vehicle is manufactured to California emissions standards, it may not physically use a converter that is cataloged as Federal emissions only.) You need to reference your Vehicle Emission Control Information (VECI) label before purchasing a Walker converter. A vehicle licensed in the State of California must use a CARB-compliant converter.

Q: The internals of my catalytic converter have melted down after a few months after installation on my vehicle. Was my converter faulty from the factory?

A: No. Converter meltdown is primarily attributed to an engine misfire. The unused air and fuel resulting from an engine misfire will cause an intense fire inside the catalytic converter, damaging it internally. Normal operating temperatures of a converter are 500-800°F, and up to 1200°F when the vehicle is under heavy load. To melt the catalytic converter's substrate, the temperature inside the converter would have to exceed 2000°F. 

Q: Will replacing my converter with a new one eliminate the P0420/P0430 code from coming on?

A: There is no guarantee that replacing the converter will keep a fault code from coming back. If an engine performance issue exists, and it has not been repaired, the P0420/P0430 fault code may recur.

Q: Why did my converter fail?

A: Typically, converter failures fall in to one of the following categories:

  • Physical damage due to corrosion, or from the converter encountering a large object on the road surface.

  • Contamination due to excessive oil consumption, internal coolant leak, or excessive carbon buildup.

  • Melted substrate due to engine misfires, leading to excessive converter temperatures.

  • Thermo-quenching where the hot converter is cold-quenched when driving through deep water or deep snow.

  • Converter aging/lack of engine maintenance - cycles of damaging engine conditions will eventually deteriorate converter performance.

Q: Why is my "Check Engine" or "MIL" light indicating that I have a "P0420 Low Converter Efficiency" code; does this mean the converter needs to be replaced?

A: A P0420 low efficiency code does not always indicate that the converter needs to be replaced. On newer vehicles, a low efficiency code can occur if the exhaust feed gases are not of the proper balance to allow the converter to operate efficiently. An experienced emissions service provider may be able to identify and resolve this concern with a scan tool; however, the most effective way for most service provider to diagnose this condition is through the use of a 5-gas analyzer.

Q: Are there any steps that a service provider can take to prevent a new converter from failing prematurely?

A: Yes. Follow these steps:

  • Since converters are designed to last the life of the vehicle, the technician should identify and correct the root cause of the original converter failure. 

  • The service provider should make sure any other codes are corrected prior to installing the new converter. This is especially true for misfire, mass air flow, rich/ lean conditions, and O2 response rate codes. 

  • The service provider should check for emissions-related Powertrain Control Module (PCM) re-flash updates. If any are available, the PCM should be updated. 

  • Pressure check the cooling system to test for internal leaks, which may contaminate the new converter.

  • Repair any exhaust leak that may be present. An exhaust leak may affect converter and O2 sensor operation.

  • Check O2 operation - The front sensor should have good frequency, amplitude and response rate and average 450mv. The rear should be fairly steady at idle equal to or above 450mv (typically 650-850mv).

  • If both of the above O2 sensor readings are not present, the vehicle should be checked with a 4- or 5-gas analyzer and repairs should be performed.



The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

Related Stories