Catalytic converters are designed to heat toxic gas molecules until their bonds break and they fall apart. However, certain malfunctions can overheat the converter and cause it to glow red. This situation is dangerous and can lead to a car fire.
Modern converters utilize two honeycomb-like ceramic blocks containing thousands of tiny passages. The passages of the first honeycomb are coated with platinum and rhodium, which pulls nitrogen away from oxides of nitrogen and re-forms it into nitrogen gas and oxygen. The oxygen gets trapped in the platinum/palladium material inside the second honeycomb, where it combines with unburned fuel in a combustion event that produces heat and carbon dioxide.
The primary cause of converter overheating is an over-abundance of fuel in the exhaust stream. The fuel enters the second ceramic block and burns there, creating excess heat. As temperatures soar to over 1,500 degrees, the ceramic matrix cracks and collapses on itself. This collapse blocks the exhaust, storing even more heat and causing further overheating. This results in a self-sustaining cascade effect of overheating known as "converter melt-down."
Several situations can cause your engine to run "rich" and introduce excess fuel into the converter. These situations include an oxygen sensor malfunction, engine misfire, improper choke or idle air control (IAC) valve operation, fuel injector leakage and computer malfunction.
