How can I tell if I need to replace my catalytic converter?

The catalytic converter is a crucial component of your vehicle's exhaust system, responsible for reducing harmful emissions. If your catalytic converter is malfunctioning, it's essential to address the issue promptly. Here's how you can tell if you need to replace your catalytic converter.

Signs of a Failing Catalytic Converter

There are several telltale signs that your catalytic converter may be failing or in need of replacement. These include:

• Reduced Fuel Efficiency: A malfunctioning catalytic converter can cause your vehicle to consume more fuel, leading to a noticeable decrease in fuel efficiency.


• Difficulty Accelerating: If your catalytic converter is clogged or damaged, it can restrict the flow of exhaust, making it harder for your vehicle to accelerate.


• Unusual Exhaust Sounds: A failing catalytic converter may produce unusual noises, such as rattling or a metallic sound, coming from the exhaust system.


• Check Engine Light: The check engine light on your dashboard may illuminate, indicating a problem with the catalytic converter or the overall exhaust system.


• Foul Odor from the Exhaust: A malfunctioning catalytic converter can cause a rotten egg-like smell to come from the exhaust, which is a sign of increased sulfur emissions.

If you notice any of these signs, it's essential to have your vehicle inspected by a qualified mechanic to determine the root cause and whether the catalytic converter needs to be replaced.

Diagnosing a Catalytic Converter Issue

To diagnose a catalytic converter issue, a mechanic will typically perform the following steps:

• Scan for Error Codes: The mechanic will use a diagnostic tool to scan for any error codes related to the catalytic converter or the exhaust system.


• Perform a Visual Inspection: The mechanic will visually inspect the catalytic converter for any signs of damage, such as cracks, discoloration, or excessive heat damage.


• Conduct a Backpressure Test: The mechanic will measure the backpressure in the exhaust system to determine if the catalytic converter is clogged or restricted.


• Measure Converter Efficiency: The mechanic may use a specialized tool to measure the efficiency of the catalytic converter, which can help determine if it needs to be replaced.

Based on the diagnostic findings, the mechanic will be able to recommend the appropriate course of action, which may include catalytic converter replacement or other necessary repairs.

Replacing the Catalytic Converter

If the diagnostic tests confirm that the catalytic converter needs to be replaced, the mechanic will typically follow these steps:

• Disconnect the Exhaust System: The mechanic will disconnect the exhaust system from the catalytic converter to access and remove it.


• Remove the Catalytic Converter: The mechanic will remove the old catalytic converter, which may involve cutting or unbolting it from the exhaust system.


• Install the New Catalytic Converter: The mechanic will install the new catalytic converter, ensuring a proper fit and secure connection to the exhaust system.


• Reconnect the Exhaust System: The mechanic will reconnect the exhaust system to the new catalytic converter and ensure a tight, secure connection.


• Perform a Final Inspection: The mechanic will perform a final inspection to ensure the new catalytic converter is installed correctly and the exhaust system is functioning properly.

Replacing a catalytic converter can be a complex and costly repair, so it's essential to address any issues with the catalytic converter promptly to avoid further damage to your vehicle's exhaust system.

Is replacing a catalytic converter worth it?

Yes, replacing a catalytic converter is often worth it because it's essential for legal and safe operation, restores engine performance, and prevents further engine damage. Driving without a working converter is illegal in many states, will cause your car to fail emissions tests, and can lead to reduced acceleration, poor fuel economy, and potential damage to your engine from overheating or backpressure issues. 
This video explains the cost difference between OEM and aftermarket catalytic converters: 51sKenny GillisYouTube · May 8, 2023
Reasons to replace a catalytic converter

• Legality and emissions: Many states require functioning catalytic converters to pass emissions tests and register your vehicle. Driving without one is illegal and can result in fines. 
• Engine performance: A failing converter can cause a noticeable drop in performance, including sluggish acceleration and reduced power. 
• Engine longevity: A clogged converter creates backpressure, which can strain the engine. It can also lead to overheating and further damage from unburned fuel or contaminants. 
• Environmental impact: The converter's primary purpose is to convert toxic gases into less harmful ones. A bad converter releases pollutants into the air. 
• Fuel economy: A properly functioning converter helps the engine run more efficiently, which can improve fuel economy. 

When to consider replacement

• Engine codes: A check engine light often indicates a problem with the catalytic converter (e.g., DTC code P0420). 
• Physical signs: You might hear a rattling noise from the exhaust or see dark smoke coming from your tailpipe. 
• Performance issues: Noticeable power loss, slow acceleration, or engine misfires are all signs that the converter may be failing. 

This video discusses the potential issues with aftermarket catalytic converters: 1mADVANCED LEVEL AUTOYouTube · May 3, 2021
Factors that influence the decision

• Extent of damage: A small crack might be repairable, but significant internal damage or a complete blockage requires replacement. 
• Repair vs. replacement: While repairs can be cheaper upfront, a replacement provides long-term reliability and ensures you meet emissions standards. A failed cleaning attempt can sometimes cost as much as a new one. 
• Cost: The cost varies based on the vehicle, type of converter (OEM vs. aftermarket), and labor costs. However, the cost of potential engine damage and failing to pass inspection often makes replacement the more cost-effective choice in the long run. 

This video shows a step-by-step process for replacing a catalytic converter: 55sScrew This!YouTube · Aug 9, 2023

What are the signs that a catalytic converter needs to be replaced?

Signs that a catalytic converter needs replacement include a Check Engine light, poor engine performance (like sluggish acceleration and low fuel economy), rattling noises from the exhaust, and a rotten egg or sulfur smell from the exhaust. A failed emissions test and visible damage, such as a glowing red converter, are also indicators of a failing converter.
 
Performance and operational issues

• Check Engine light: The most common sign, as the vehicle's computer detects a problem with emissions or oxygen sensors. 
• Poor acceleration and performance: A clogged converter restricts exhaust flow, leading to sluggish acceleration, a loss of power, and a reduced ability to reach higher speeds. 
• Engine misfires: A failing converter can cause the engine to misfire, which can be felt as a rough idle or hesitation. 
• Decreased fuel economy: With reduced engine efficiency, your vehicle may start to use more fuel than it used to. 

Smells and sounds

• Rotten egg or sulfur smell: This indicates that the converter is not properly converting hydrogen sulfide, a common symptom of a failing unit.
• Rattling noises: If the internal honeycomb structure of the converter breaks apart, it can cause a rattling or clunking sound, particularly when the engine is on or when you start your vehicle. 

Visual and environmental indicators

• Failed emissions test: The primary function of a catalytic converter is to clean emissions, so if it's not working, your vehicle will likely fail an emissions test. 
• Excessive heat: A clogged converter can cause the exhaust to become excessively hot. A converter that is glowing red is a clear sign of a major blockage. 
• Black smoke: Unburnt fuel can lead to black smoke coming from the tailpipe. 

How to test if your catalytic converter is bad?

You can test a catalytic converter with a few methods: check for performance symptoms like poor acceleration or fuel economy, and a "rotten egg" smell. For a more direct test, use an infrared thermometer to compare the inlet and outlet temperatures (the outlet should be hotter), or use a vacuum gauge or backpressure tester to check for exhaust restrictions. 
Symptoms to look for

• Performance issues: Sluggish acceleration, engine misfires, or difficulty accelerating past a certain speed can indicate a restriction. 
• Decreased fuel economy: A clogged converter creates backpressure, forcing the engine to work harder and use more fuel. 
• "Rotten egg" smell: A sulfur or rotten egg smell from the exhaust means the converter isn't working properly. 
• Illuminated Check Engine light: This is often the first sign, and a code like P0420 may be stored. 
• Engine overheating: A blocked converter can prevent exhaust gases from escaping, causing the engine to run hotter. 
• Rattling noise: Shaking the vehicle while it's on a lift can reveal internal damage if you hear a rattling sound. 

DIY tests

• Infrared thermometer test:
  • Drive the car for about 15 minutes to get it to operating temperature. 
  • Use an infrared thermometer to measure the temperature of the pipe right before and right after the catalytic converter. 
  • The outlet should be about $100$°F to $200$°F hotter than the inlet; if it's not, the converter may be failing. 
• Vacuum gauge test:
  • Attach a vacuum gauge to a suitable port on the intake manifold. 
  • At idle, the vacuum should be steady (around 17−2117 minus 2117−21 inches). 
  • Rev the engine to about 250025002500 RPM. The vacuum should either remain stable or increase. A significant drop indicates a blockage. 
• Backpressure test:
  • Remove an oxygen sensor and connect a backpressure tester to the exhaust manifold. 
  • At idle, the pressure should be less than 111 PSI. At 250025002500 RPM, it should not exceed 333 PSI. If it exceeds this, there is a restriction. 
• Physical inspection:
  • If you have access, carefully remove the oxygen sensor before the converter and look inside with a flashlight. If you see that the honeycomb material is broken or falling apart, the converter is bad. 

1:34Tips For Diagnosing A Bad Catalytic ConverterYouTubeCrossroad Garage · 8mo 0:44How to Test a Catalytic Converter Easy DIY Guide 2YouTubeAuto Repair Tips · 1y 1:01Signs of a Failing Catalytic Converter ExplainedTikToktrqautoparts · 1w 1:42Is my catalytic converter bad? : r/MechanicAdviceReddittrhb · 2y 0:16I'm suspecting a clogged catalytic converter, does this vacuum test ...RedditHitlersSpecialFlower · 4y (function(){
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How does a car act when the catalytic converter is going out?

Symptoms of a bad catalytic converter include a Check Engine light, a sulfur or "rotten egg" smell from the exhaust, poor engine performance like reduced acceleration and fuel economy, and a rattling noise from under the vehicle. Other signs are engine misfires, difficulty starting the car, and failing an emissions test.
 
Performance and starting issues

• Poor acceleration: A clogged converter restricts exhaust flow, making the engine struggle to accelerate. 
• Reduced engine performance: You may notice a lack of power, a rough idle, or a hesitation to accelerate. 
• Engine misfires: Incomplete combustion can cause the engine to misfire. 
• Difficulty starting: A severely clogged converter can block exhaust gases completely, potentially preventing the engine from starting or causing it to stall. 

Smells and sounds 

• Sulfur or rotten egg smell: This is a classic sign, as a failing converter can't properly convert hydrogen sulfide into a less offensive odor.
• Rattling noise: Internal components of the converter can break apart and rattle, especially when the engine is running or when the vehicle is moving. 

Other indicators

• Check Engine light: This is a common warning that a sensor has detected a problem with the emissions system. 
• Failed emissions test: A faulty converter cannot properly clean exhaust gases, which will cause a failure during an emissions inspection. 
• Poor fuel economy: When the engine has to work harder to overcome the restricted exhaust, it uses more fuel.