If your catalytic converter needs replacing, then it is highly probable that at least one of the six causes below has contributed to its failure.


An Oxygen Sensor is Not Functioning Properly.
An oxygen sensor failuring can lead to incorrect readings of exhaust gasses. A faulty sensor can cause a too lean or too rich condition. Too rich and the catalyst can meltdown. Too lean and the converter is unable to convert the hydrocarbons into safe elements and the catalytic converter may not pass a state SMOG inspection.


You Have Deteriorated Spark Plug and/or Spark Plug Wires.
Spark plugs that misfire cause unignited fuel to enter the exhaust system. The unburned fuel then later ignites inside the catalytic converter and could result in a meltdown of the ceramic catalyst. Spark plugs and spark plug wires should be checked regularly and replaced if damaged or if wires show wear or cracking.


You Have Incurred Road Damage or Have Broken Hangers.
The catalyst inside a catalytic converter is made from a lightweight, thin-walled ceramic. It is protected by a dense insulating mat. This mat holds the catalyst in place and provides protection against moderate damage. However debris striking the exterior of the converter, or improper or broken exhaust system hanger support can cause a Catalyst Fracture. Once the ceramic catalyst is fractured, the broken pieces loosen and rattle around and break up. Flow is interrupted and back-pressure in the exhaust system increases. This leads to heat build-up and loss of power. Possible causes of a catalyst fracture are road debris striking the converter, loose or broken hangers, potholes, or off-road driving.


Oil and/or Antifreeze are Entering Your Exhaust System.
Either oil or antifreeze entering the exhaust system can block the air flow by creating a heavy carbon soot that coats the ceramic catalyst inside the catalytic converter. These carbon deposits create two problems. First, the deposits prevent the catalytic converter from reducing harmful emission in the exhaust flow. And second, the carbon deposits clog the pores in the ceramic catalyst and block exhaust flow, increasing back-pressure and causing heat and exhaust to back up into the engine compartment. Your engine may actually draw exhaust gasses back into the combustion chamber and dilute the efficiency of the next burn cycle. The result is a loss of power and overheated engine components. Possible causes are worn piston rings, failing gaskets, faulty valve seals, or warped engine components.


Excess Fuel is Entering Your Exhaust.
Your fuel is meant to burn in the combustion chamber only. Any fuel that leaves the combustion chamber unburned will enter the exhaust system and ignite when it reaches the catalytic converter. This can overheat the catalytic converter far above normal conditions and cause it to melt down. Probable causes are a faulty oxygen sensor, an out-of-spec fuel mixture, incorrect timing, malfunctioning spark plugs, a sticking float, a faulty fuel injector, or a malfunctioning check valve.


An Engine Tune-Up is Required.
A number of problems could occur to the catalytic converter as the result of an engine that is out of tune. Any time an engine is operating outside its proper specifications, unnecessary wear and tear may be caused to the catalytic converter (as well as the engine itself). The damage is often the result of an incorrect misfiring spark plugs, air/fuel mixture, or incorrect timing. Any of these conditions could lead to catalytic converter failure.