The Inside Story of Your Catalytic Converter: Causes of Catalytic Converter Failure

With the advent of emission control regarding vehicle exhaust came the need to ‘scrub’ environmentally harmful gases before emitting the products of combustion into the atmosphere. Your Catalytic Converter , part of the vehicle’s exhaust system, is designed to either reduce or oxidize (through chemical reaction) the noxious gases using catalysts. Should your “Check Engine” light be illuminated, chances are there is a problem with your catalytic converter – it is essential that the expert technicians at Everett Catalytic Converter diagnose and repair your exhaust system immediately!

Although emission control is not monitored in every county in Washington state, by doing your part, voluntarily, emissions testing may never be necessary. Think about it: if every vehicle owner were to assure proper operation of the catalytic converter(s) – collectively, vehicle emissions will remain low enough that testing becomes irrelevant. Understanding the elegant design of a catalytic converter is recommended to grasp the true value of how this component helps to clean the world’s air. Just as important is learning the primary reasons for catalytic converter failure.

The internal core, or substrate, of a catalytic converter is often the component that fails. Although the housing is vulnerable to damage as well. The 4 most common reasons for catalytic converter failure include:


1. Overheated Substrate

A substrate that is overheated for extended periods of time will eventually melt and/or fail. The most common causes of substrate melting/overheating are:

  • Worn or failed O2 sensor causing poor fuel control
  • Air cleaner restricted
  • Fuel quality is substandard
  • Engine load is excessive
  • Inadequate engine compression
  • Inadequate spark
  • Weak ignition
The substrate overheats when combustion within the engine is too rich, operating at a higher than normal temperatures. When the substrate fails by overheating or melting, your car will exhaust excessive:
  • Hydrocarbons
  • Oxygen (O2)
  • Carbon Monoxide (CO)
Should your vehicle’s catalytic convertor have a melted substrate or be showing signs of substrate overheating it is crucial that the underlying problem be diagnosed and repaired immediately!
2. Substrate Poisoning
There are several things that are poisonous to the substrate of a catalytic convertor:
  • Leaded Gasoline – using in a vehicle with a catalytic converter will cause catastrophic damage; the fuel lines must be flushed or replaced should this happen.
  • Antifreeze – if present in the exhaust system indicates a leaks within both the cooling and the exhaust system, the leaks must be located and repaired immediately. Cross-contamination can cause severe damage to both systems.
  • Zinc (present in some oil additives) – carefully read all labels to insure no zinc is present
  • Certain silicon sealants – carefully read all labels to insure no zinc is present
3. Substrate Coated with Oil
The presence of oil either on or in a catalytic converter’s substrate can indicate a leak in the vehicle’s engine. A common symptom of this is a dramatic increase in oil consumption. Your car using increasing amounts of oil could be a result of excessive engine wear. Please note: the underlying cause of the problem must be remedied before replacing an oil coated/plugged catalytic converter substrate. Which, in this case, would include repair/replacement of your vehicle’s engine.
4. Structural Damage to Catalytic Converter
A catalytic converter can be damaged in a variety of ways. Denting is very common from potholes or collision damage. External damage to catalytic converters can also result from:
  • Metal fatigue from heating/cooling cycle of engine use in winter conditions (quenching action of driving through cold water when engine is operating at normal temperature)
  • Corrosion from chemicals like road salt
  • O2 sensor plug not operating properly (stripped)
  • Pipe joint failure at either/or the inlet and outlet
Each of these conditions is potentially hazardous and must be evaluated and repaired immediately.