Catalytic Converter Failure Symptoms

by Alexis Writing

A catalytic converter is a device meant to reduce the extent of impurity in a vehicle's emissions. The converter can fail because of internal damage or external factors such as mishandling, improper fitting or accidents.

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Loss of Power

A loss of power is the surest symptom that something has gone wrong with the catalytic converter. This happens when there is overheating or thermal failure. Typically, this occurs when an excess of raw or unused fuel comes into contact with the converter, and burns in the converter itself. The fuel does not reach the engine. When this leakage occurs, the high amount of fuel can also heat up the converter too much, leading to a burnout of the ceramic monolith (a part of the converter).

High Emissions Levels

High emissions levels happen when the converter fails as a result of contaminated or plugged substrates. This leads to a disproportionately higher than required mixture of fuel. When oil or antifreeze or radiator sealant enters the exhaust flow, the air mixture becomes excessive, which leads to carbon deposits in the exhaust. Whenever the engine is turned on and the accelerator pushed, the vehicle emits high levels of substances such as hydrocarbons, carbon monoxide and nitrogen oxide.


Rattling is a result of thermal shock. This happens when the converter, after reaching a full state of heating, suddenly comes into contact with a cooling agent of extreme temperature, such as snow. The extreme change in temperature results in cracking of the ceramic substrate. The converter housing then contracts on account of this change. This causes the rattling sound when the now-compact converter comes into contact with another substance.

Foul Odor

A foul odor is another symptom of catalytic converter damage or failure. When there is excessive heating in the ceramic monolith due to the wrong fuel or a fuel mixture that is too rich, the converter can become damaged. The improper fuel mixture can result in too much hydrogen sulfide in the emissions, resulting in the converter giving off the odor of rotten eggs.

Other Symptoms

When the vehicle runs over road debris or suffers damage due to an accident or a collision, there could be a variety of changes in performance of the converter. These symptoms differ depending on the nature of the damage to the converter.

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