A clogged catalytic converter can present several noticeable signs, like an illuminated check engine light, poor engine performance, unusual smells, strange noises, and overheating.
Here’s a closer look at the symptoms:
- Lit check engine light: This is often the first warning and may signal that the converter isn’t operating efficiently.
- Reduced engine performance: The car may struggle to accelerate, feel underpowered, or run roughly at idle.
- Sulfur or rotten egg smell: A distinct exhaust odor indicates that the catalytic converter is clogged and isn’t properly processing harmful gases.
- Rattling sounds: Loose or broken internal parts can cause a metallic rattling, especially when starting or driving.
- Engine misfires and poor fuel economy: A clogged converter makes the engine burn more fuel than usual, often leading to misfires and eventually lowering the gas mileage.
- Overheating: Trapped exhaust gases can cause excessive heat to build up under the car.
- Dark exhaust smoke: Unburned fuel may exit the exhaust pipe as dark or sooty smoke.
- Difficulty starting: Severe blockages can make it harder for the engine to turn over.
- Failed emissions test: A faulty converter allows excess pollutants to pass through the exhaust.
If you notice these symptoms, get a qualified mechanic to check your car’s catalytic converter. Even better, our expert technicians at AutoNation Mobile Service can come to you, diagnose the issue, and carry out the necessary repairs from your driveway.
Want to know more about clogged catalytic converters?
Keep reading to explore each symptom and the diagnostic steps in detail.
This Article Contains:
- 9 Unmissable Signs of a Clogged Catalytic Converter
- How Does a Catalytic Converter Get Clogged?
- Can You Continue Driving with a Clogged Catalytic Converter?
- How to Diagnose a Clogged Catalytic Converter (3 Methods)
- Can You Clean a Clogged Catalytic Converter Instead of Replacing it?
- 3 FAQs about Catalytic Converters
9 Unmissable Signs of a Clogged Catalytic Converter
The catalytic converter contains a honeycomb-shaped core coated with special metals that help break down harmful gases like carbon monoxide into less toxic gases before they exit the vehicle.
When this honeycomb gets clogged, you’ll notice the following symptoms:
1. Illuminated Check Engine Light
If your check engine light is on, you can use an OBD scanner to determine whether the catalytic converter is the cause.
A clogged unit may often trigger one of these codes:
- P0420: Catalyst System Efficiency Below Threshold (Bank 1)
- P0430: Catalyst System Efficiency Below Threshold (Bank 2)
Both codes mean the vehicle’s computer has detected that the catalytic converter isn’t working as efficiently as it should.
2. Trouble Starting the Car
A failing catalytic converter creates a blockage in the exhaust system, trapping gases that should be exiting through the tailpipe. This creates a backpressure, preventing enough fresh air from entering the combustion chamber, leading to incomplete combustion.
As a result, you may notice stalling, sputtering, difficulty starting, or sluggish performance. In severe cases, unburned fuel can cause dark smoke from the exhaust.
3. Poor Acceleration
If your vehicle jerks, stalls, or struggles on steep hills, it could be due to backpressure buildup caused by a clogged CAT converter. This buildup leads to incomplete combustion and reduces engine power.
4. Sulfur and Rotten Egg Smell
When gasoline passes through a working catalytic converter, it converts hydrogen sulfide (a harmful emission) into odorless sulfur dioxide.
However, a clogged CAT can’t correctly process the sulfur gases, resulting in a rotten egg smell from the exhaust.
5. Rattling Noise
A rattling sound under your car while starting, idling, or driving often means the honeycomb structure inside the catalytic converter has broken apart due to heat or damage.
When this happens, pieces inside the converter move around and create the noise. A rich fuel mixture can also cause extra buildup, causing the rattling to worsen over time.
6. Engine Misfires and Poor Fuel Economy
A clogged catalytic converter creates backpressure that disrupts combustion and can trigger misfires. This can eventually damage critical components like the spark plugs, ignition coils, and piston rings.
Since the blockage also reduces the oxygen in the combustion chamber, it forces the engine to work harder to maintain speed, which affects your fuel economy.
7. Heat Coming from Under the Car
When a CAT’s passages are blocked, exhaust gases can’t move through freely, trapping heat inside the unit. This heat can then radiate through the vehicle’s floor, warming the cabin, and may also be noticeable when you stand near the car.
8. Engine Overheating
Restricted airflow from a clogged CAT forces heat and exhaust gases to stay inside the engine. This quickly raises engine temperature and can lead to frequent overheating — noticeable on the temperature gauge.
9. Failed Vehicle Emission Test
Most US states require vehicle owners to undergo an annual exhaust gas emissions test.
If your catalytic converter isn’t working properly, it won’t reduce harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides to safe levels. Consequently, your car will fail an emissions test until you replace the part.
Now that we’ve gone over the symptoms, let’s understand why your catalytic converter clogs in the first place.
How Does a Catalytic Converter Get Clogged?
Here are four common reasons a catalytic converter can become clogged:
- Normal wear and tear: The ceramic core can break apart over time, and the loose pieces can block exhaust flow.
- Using poor-quality fuel: Low-grade fuel often contains contaminants that don’t burn off completely, leaving deposits inside the converter.
- Excess unburned fuel: When too much fuel enters the engine, it can ignite inside the catalytic converter, leaving unburned hydrocarbon deposits on the honeycomb and clogging it. This can also lead to frequent engine misfires, further damaging the converter.
- Oil or coolant leaks: Engine leaks allow oil or coolant to enter the exhaust system, which can coat and clog the converter’s honeycomb structure.
Next, let’s understand what happens if you drive with a clogged CAT converter.
Can You Continue Driving with a Clogged Catalytic Converter?
No. When clogged, a catalytic converter traps exhaust gases and builds up excess heat, which can damage its internal coating, melt the core, and eventually destroy the unit. This leaves replacement as the only option.
Remember: A catalytic converter is quite expensive to replace.
But that’s not all!
This restriction also forces the engine to work harder, interfering with the ECU and oxygen sensors. As a result, it leads to poor fuel efficiency and puts added strain on critical components like spark plugs, ignition coils, and piston rings.
Want to know how a mechanic will diagnose a faulty unit?
Let’s find out.
How to Diagnose a Clogged Catalytic Converter (3 Methods)
While there are several ways to check if a catalytic converter is clogged, these tests often require specialized tools, technical know-how, and a safe work environment. That’s why it’s best to let a professional mechanic perform them.
Here are the three tests they may conduct to diagnose a clogged converter:
1. Vacuum Test:
- Get a vacuum gauge and set the car to neutral or park.
- Connect the vacuum gauge to a direct vacuum line, like the direct intake manifold.
- Start the car and allow it to idle until it reaches prime operating temperature.
- The vacuum gauge should return a reading of 18-22 inches.
- Start accelerating and allow the car to reach around 2500-3000 revolutions per minute (RPM).
- The vacuum gauge reading should reduce before returning to the previous level. If it takes a long time, you likely have a bad catalytic converter.
2. Temperature Test:
- Keep an infrared or kitchen thermometer ready.
- Start the car and let it reach an optimal operating temperature. To do this, they may take it for a short drive.
- Set the vehicle to park or neutral.
- Measure the temperature at the inlet pipe connecting to the front of the catalytic converter. Repeat the same for the outlet pipe by connecting to the rear of the converter.
- If inlet and outlet temperatures match, the catalytic converter is likely faulty.
3. Back Pressure Test:
- Get a back-pressure gauge.
- Remove the front oxygen sensor and replace it with a back pressure gauge.
- Start your car, rev the vehicle at 2,000 RPM, and note the back pressure gauge’s reading. A reading between 0 and 3 pounds per square inch (PSI) is normal.
- If the reading is around 8 PSI, your catalytic converter is clogged.
- Finally, they’ll reinstall the oxygen sensor.
If the diagnosis confirms you have a catalytic converter problem, your mechanic may recommend a replacement.
Now you must be wondering…
Can You Clean a Clogged Catalytic Converter Instead of Replacing it?
Yes, it’s possible to clean a clogged unit. However, the method you use depends on the severity of the catalytic converter problem.
Here are some options:
- Use a cleaning agent: For mild clogs, pour a catalytic converter cleaner into your fuel tank by following the instructions on the bottle. You can also use a lacquer thinner (1 gallon in a half-full gas tank). Then, run the engine at high RPM for about 30 minutes to help flush out light deposits.
- Add fuel additives or change fuel type: If the catalytic converter cleaner doesn’t work, switch to a higher-quality fuel or add a fuel additive. High-octane fuel burns cleaner, while additives can help break down deposits and reduce future buildup.
- Manually wash the converter: For stubborn clogs, you’ll need to remove the converter to clean it, so it’s best to let a mechanic handle it. Here’s what they’ll do:
- Park in a safe, well-lit place, turn off the engine, and let the converter cool completely.
- Wear gloves and goggles.
- Unbolt the converter using a wrench or hex key.
- Next, use either of the two methods:
- Pressure wash: Use a pressure washer to flush water through both ends of the converter, then let it dry completely.
- Soak: Place it in hot water with degreaser or detergent, rinse well, and dry before reinstalling.
NOTE: Using the pressure washer or soaking method won’t help if the converter is damaged or completely blocked. In that case, replacing it is the only option.
Got more questions?
Check out the FAQs next.
3 FAQs about Catalytic Converters
Here are the answers to commonly asked questions about catalytic converters:
1. How Long Does a Catalytic Converter Last?
The average lifespan of a catalytic converter is about 100,000 miles or around 10 years.
That said, regular car maintenance, engine check-ups, and timely oil filter changes can extend the lifespan of your catalytic converter and engine.
2. How Can You Keep Your Catalytic Converter from Clogging?
To avoid clogs, follow your car maintenance schedule and these simple steps:
- Replace spark plugs when needed: A spark plug in good condition ensures clean combustion and prevents unburned fuel from reaching the exhaust.
- Schedule regular engine checks: Fixing problems like misfires, fuel injector faults, or exhaust leaks can reduce strain and prevent CAT converter failure.
- Add fuel additives occasionally: Fuel system cleaners can break down and remove buildup before it causes blockages.
3. How Much Does a Catalytic Converter Replacement Cost?
Replacing a bad catalytic converter can cost around $450 to $4,200.
This includes:
- Parts: $300 to $4,000
- Labor: $150 to $200
The exact price depends on your car’s make and model, engine type, parts quality, and whether your insurance covers part of the expense.
Fix Catalytic Converter Issues with AutoNation Mobile Service
A failing catalytic converter can impact vehicle performance and, if ignored, lead to severe and expensive damage. The best way to protect your vehicle and wallet is to act quickly when you notice any warning signs.
If you suspect a problem, contact AutoNation Mobile Service.
Our expert mobile technicians are available seven days a week, and back every repair with a 12-month, 12,000-mile warranty for added peace of mind.
Schedule your service today and keep your car running at its best.