The three most common failures of a catalytic converter are clogging (blockage), overheating and catalyst poisoning. Explaining more specifically, over time, a catalytic converter can become clogged or blocked due to the accumulation of contaminants. They normally are unburned fuel, oil, or coolant. Overheating of the catalytic converter can result from unburned fuel entering the exhaust system, a misfiring engine, or other issues causing excessive heat. Overheating can lead to internal damage and reduced efficiency. Catalytic converter “poisoning” means it being exposured to certain contaminants, such as lead, phosphorus, or silicon. They can “poison” the catalyst within the converter, reducing its ability to facilitate the necessary chemical reactions for emission control.