Signs of a Failing Catalytic Converter

What Is a Catalytic Converter?

A catalytic converter is part of your vehicle’s exhaust system. It converts harmful gases, like carbon monoxide, hydrocarbons, and nitrogen oxides, into less harmful substances such as carbon dioxide and water vapor.

When a catalytic converter is working properly, it helps reduce your car’s environmental impact. However, over time it can become clogged, contaminated, or damaged, leading to performance issues.

Signs of a Failing Catalytic Converter

1. Decreased Engine Performance

One of the earliest and most noticeable signs of a failing catalytic converter is a reduction in engine performance.

If your vehicle struggles to accelerate, feels sluggish, or has difficulty maintaining speed, the catalytic converter might be clogged or restricted. When this happens, exhaust gases can’t exit the engine efficiently, causing a loss of power.

2. Poor Fuel Efficiency

Have you noticed that you’re visiting the gas station more frequently? A failing catalytic converter can decrease fuel efficiency because the engine must work harder to push exhaust gases through a clogged or damaged converter. As a result, your vehicle burns more fuel than usual.

3. Illuminated Check Engine Light

The check engine light can turn on for various reasons, but one culprit may be a failing catalytic converter.

Modern vehicles are equipped with oxygen sensors that monitor emissions (measure the amount of oxygen in the exhaust). If the sensors detect irregular exhaust gas levels, they will trigger the check engine light. A diagnostic scan can reveal if the catalytic converter is the cause. Further testing may be required, but by using a scan tool, it points the mechanic in a direction for proper diagnosis. (whether the catalytic converter is bad, an exhaust leak is present or whether an oxygen sensor is sending the proper signal to the powertrain control module (PCM).

4. Rattling Noises

If you hear a rattling sound coming from underneath your vehicle — especially during startup — it could indicate a damaged catalytic converter. The internal honeycomb structure (substrate) of the converter can break apart over time due to excessive heat, impact damage or whether the engine is running too rich (too much gas to the amount of air). When this happens, the loose pieces can create a distinct rattling noise and may restrict the exhaust flow.

5. Failed Emissions Test

A failing catalytic converter often causes your car to release higher levels of harmful pollutants. This usually results in a failed emissions test, which is required in many states for vehicle registration. If your vehicle doesn’t pass, many times the catalytic converter is often to blame.

6. Sulfur or Rotten Egg Smell

A distinct smell of sulfur or rotten eggs coming from your exhaust is another telltale sign of a failing catalytic converter. This usually means the engine is running rich and needs to be addressed as well and especially right after the catalytic converter is replaced. If the rich condition is not corrected, it will ruin the new catalytic converter and will void any warranty of converter.

This odor indicates that hydrogen sulfide in the exhaust is not being properly converted to odorless sulfur dioxide, which can happen when the converter becomes contaminated or is no longer functioning efficiently.

What to Do If You Suspect a Failing Catalytic Converter

If you experience any of the signs mentioned above, it’s important to act quickly.

Your next step should be at your trusted mechanic. Bring your vehicle to a certified mechanic or a reputable auto shop like Northwest Auto Houston. A professional can perform a diagnostic test to confirm whether the catalytic converter is the problem or if another component is causing the issue.

A failing catalytic converter is more than just a nuisance — it’s a serious issue that can impact your vehicle’s performance, fuel economy, and emissions. By learning to recognize the early warning signs, you can take proactive steps to protect your engine and avoid costly repairs down the road.

If you suspect your vehicle is showing signs of a failing catalytic converter, don’t wait. Schedule a diagnostic appointment with Northwest Auto Houston today and let our expert technicians help you get back on the road with confidence. Give us a call at (281) 894-8880.

We are always here to help in any way we can!