A catalytic converter will rarely fail without a problem or malfunction occurring somewhere in the emission system in front of the converter. It is extremely important to determine what caused the catalytic converter to fail so that the problem can be fixed and to prevent a recurrence of the failure.



Catalyst Fracture.
This is an example of a catalyst fracture. The ceramic became loose, cracked and has broken down. The pieces began to obstruct flow, creating back-pressure and increasing the heat in the exhaust system. There is evidence of a partial meltdown in the shown example due to overheating.

The initial cause for this damage could have been road debris striking the catalytic converter based on evidence of impact on the catalytic converter shell. In some cases, if the protective mat that holds the catalyst in place is directly exposed to exhaust gasses, it could deteriorate and allow the catalyst to fracture.



Catalytic Converter Meltdown.
This is an example of a catalytic converter meltdown. The catalytic converter was super-heated due to raw fuel dumping into the exhaust system. The excess unburned fuel ignited when it struck the hot ceramic catalyst and drove the temperature far above the normal operating parameters of the catalytic converter. The ceramic catalyst is unable to withstand the extremely high temperature and begins to melt. The ceramic collapses and the catalytic converter is destroyed. The melted ceramic may block the exhaust system air flow and cause additional damage to the engine. A catalytic converter glowing red-hot, or evidence of heat discoloration, confirms this situation.

The condition that led to this catalytic converter meltdown could be the result of a number of malfunctions including a faulty oxygen sensor, an incorrect fuel mixture, faulty spark plugs, cracked spark plug wires, faulty fuel injectors, a faulty check valve, incorrect timing, sticking float, or other ignition malfunctions.

Carbon Deposits.
This is an example of a catalytic converter with excessive carbon deposits in the ceramic catalyst. This is usually a result of oil or antifreeze entering the exhaust system or a too-rich fuel mixture. The heavy carbon deposits clog the catalytic converter and reduce exhaust air flow. These increase back-pressure and cause the entire exhaust system to heat up. The heat backs up into the engine compartment and may result in a number of heat-related engine problems.

Mild carbon depositing may do less damage to engine components but it still may seriously affect the catalytic converter’s ability to reduce toxic emissions. It could easily cause a vehicle to fail an emission test, especially in California where the SMOG tests are most stringent.

Carbon deposits may be the result of worn piston rings, faulty valves, worn gaskets, leaking gaskets, or lead in the fuel.