How your Automobile Three-Way Catalytic Converters Broken

When a three-way catalytic converter malfunctions, the following one or more symptoms usually occur:

1. Obvious power loss and weak acceleration

Symptom: The vehicle feels "weak", especially when going uphill or needing to accelerate quickly. Pressing the accelerator does not increase the speed, and the engine sounds muffled.

Cause: When the catalytic converter is clogged, it is like "covering the mouth" of the exhaust pipe, causing the engine to have poor exhaust. The exhaust cannot be discharged, and fresh air cannot fully enter the cylinder, thus affecting the combustion efficiency and resulting in power loss.

2. Abnormally high fuel consumption

Symptom: Under unchanged driving habits and road conditions, fuel consumption increases significantly.

Cause: The same reason as above, the increased exhaust back pressure causes the engine to consume more fuel to overcome the exhaust resistance to maintain power output, thus leading to increased fuel consumption.

3. Unusual odor in exhaust emissions

Symptom: The exhaust has a pungent "rotten egg" smell (hydrogen sulfide odor).

Cause: This is typically a symptom of catalytic converter failure or poisoning. When the precious metals (platinum, rhodium, palladium) inside the catalytic converter lose their activity, they cannot effectively convert the sulfides produced by fuel combustion into harmless sulfur dioxide, thus generating hydrogen sulfide.

4. Engine check light on

Symptom: The engine check light on the dashboard (usually a yellow engine icon) remains on.

Cause: The ECU (engine control unit) of modern cars monitors the oxygen content difference before and after the catalytic converter through the oxygen sensor to determine its working efficiency. If the catalytic converter efficiency is below the standard value, the ECU will trigger the check light and store the corresponding fault code (such as P0420 "catalytic converter system efficiency below threshold").

5. Failing the annual emission inspection

Symptom: During the annual inspection, the CO (carbon monoxide), HC (hydrocarbons), NOx (nitrogen oxides), etc. in the exhaust test are severely over the limit.

Cause: This is the most direct consequence of a failed catalytic converter. Its core oxidation and reduction reactions cannot proceed normally, and it cannot convert harmful gases into carbon dioxide and water.

6. Abnormal noise

Symptom: When driving on bumpy roads or gently tapping the exhaust pipe, a metallic rattling sound similar to "clattering" can be heard.

Cause: The ceramic carrier inside the catalytic converter is broken or sintered. The fragments rattle inside the shell as the vehicle moves.

Analysis of the causes of these faults

The above fault symptoms are usually caused by one or more of the following reasons:

1. Catalytic converter poisoning (chemical deactivation)

Lead poisoning: Using leaded gasoline. Lead covers the surface of precious metals, preventing them from coming into contact with exhaust gases and causing permanent deactivation. (Currently, there is no leaded gasoline in China, but be cautious of fuel quality at small gas stations.)

Sulfur, phosphorus, and zinc poisoning: These come from impurities in engine oil additives or low-quality fuel. They also contaminate precious metals and reduce their catalytic activity.

Silicon poisoning: Using substandard sealant (RTV sealant). The silicon oxides it releases at high temperatures can clog and contaminate the catalytic converter.

2. Carbon deposits and blockage (physical blockage)

Symptom: Causes increased exhaust back pressure, leading to power loss and increased fuel consumption.

Cause:

Long-term incomplete combustion in the engine: Such as insufficient spark plug ignition energy, fuel injector leakage, or overly rich air-fuel mixture, resulting in large amounts of carbon deposits entering the catalytic converter with the exhaust and blocking its honeycomb channels.

Excessive engine oil consumption (burning oil): Old or faulty engines (such as worn piston rings or valve oil seals) can burn oil. The ash produced by burning oil can clog the catalytic converter.

Long-term short-distance low-speed driving: The engine water temperature and operating temperature never reach the optimal state, easily causing carbon deposits, and the catalytic converter cannot reach its normal operating temperature (about 400-800°C), thus unable to burn off the adhered carbon deposits.

3. High-temperature sintering and melting

Symptom: The catalytic converter carrier melts, blocks, or breaks, causing severe power loss and abnormal noise.

Cause: Engine misfire: This is the most common and fatal cause. When a cylinder fails to work (such as a damaged spark plug or faulty ignition coil), the unburned fuel mixture enters the exhaust pipe and continues to burn in the hot catalytic converter, generating extremely high temperatures far exceeding 1000°C, directly melting the ceramic carrier.

Excessive fuel mixture: Excessive fuel injection causes some fuel to burn a second time in the catalytic converter, generating excessively high temperatures.

Long-term aggressive driving or towing heavy loads: The engine operates under continuous high load, resulting in persistently high exhaust temperatures.

Mechanical damage

Symptoms: Carrier fragmentation, producing abnormal noises.

Causes:

External impact: Vehicle bottoming out, hitting the catalytic converter housing.

Thermal expansion and contraction: The carrier undergoes drastic temperature changes, developing cracks, and eventually breaks under vibration.

Aging: After long-term use, the carrier material becomes brittle due to high temperatures and vibrations.

Prevention and maintenance suggestions

Use high-quality fuel and oil.

Regularly maintain the vehicle, promptly replace spark plugs, ignition coils, etc., to ensure the engine is in good working condition and avoid misfires and incomplete combustion.

If the engine check light comes on, especially accompanied by symptoms such as shaking and lack of power, immediate inspection is necessary. Do not continue long-distance driving to prevent catalytic converter damage.

Avoid frequent short trips. Occasionally, let the vehicle fully warm up and drive at high speeds to help remove some carbon deposits.

Solve the "oil burning" problem.

In conclusion, the three-way catalytic converter is a "delicate" and expensive component. Its health largely depends on the engine's working condition and the driver's vehicle usage habits. Once any of the above fault symptoms occur, it is essential to promptly visit a professional repair shop for inspection and diagnosis.