Catalytic Converter

The catalytic converter is designed to convert harmful emissions, produced by an internal combustion engine, to less-harmful elements: H2O (Water), CO2 (Carbon Dioxide) and N2 (Nitrogen).To perform this conversion, the catalytic converter works with a vehicle's PCM (Powertrain Control Module) and other emissions control devices. OBDII (On-Board Diagnostics Version 2) monitors the emissions control devices and provides feedback on their operating condition. As the EPA (Environmental Protection Agency) updates emissions standards, the OBDII system becomes more sensitive to fluctuations in emissions performance.


Any malfunction causing an unusually high level of HC or CO (in conjunction with high levels of O2) to enter the converter, will dramatically elevate its temperature.

Potential causes for high HC readings may include:
AFR Cylinder imbalance
Excessive engine or vehicle load
   - Fuel delivery system or fuel quality
   - Sluggish (worn out) O2 sensors
   - Excessive backpressure
   - Low compression
Poor spark, or weak ignition

NOTE: Temperatures in excess of 1600º F may damage catalyst, without visible signs of melting



Catalyst poisoning occurs when the converter is exposed to emissions containing substances that coat the working surfaces, enveloping the catalyst to the point it cannot contact and treat the exhaust.

Potential causes for coated or fouled substrate may include:
Excessive carbon build-up in exhaust
Internal coolant leaks (head / intake gasket)
Use of non-converter-safe gasket sealants
Excessive oil consumption (burning oil)
Improper fuels or additives (E85, diesel)



The primary cause of structural damage is road debris striking the converter. Normally, some evidence of impact is visible on the converter shield.

Other conditions that may cause structural damage:
Thermal shock
Metal fatigue
Stress fractures
Stripped O2 Sensor threads
Flex pipe failure
Air-gap pipe failure

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 the 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 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.

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 down stream 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.

In August, 1986, the U.S. Environmental Protection Agency issued new EPA converter guidelines for the construction, efficiency and installation of aftermarket converters. The converters listed in our catalog have been designed and manufactured to meet the EPA policy and emission reduction requirements. For further questions in regards to using and installing an aftermarket converter, please refer to the following EPA document

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, high sulfur fuel, and/or rich fuel mixtures forming carbon deposits can quickly coat the substrate preventing it from working effectively.

No. Converter meltdown is primarily contributed 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.

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

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

Contamination - due to excessive oil consumption, internal coolant leak, or excessive carbon build up.

Melted substrate - due to engine misfires which lead to excessive converter temperatures.

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

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

Yes, 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 technician 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. Pressure check the cooling system to test for leaks which will 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 and 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.

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