Catalytic Converter Rattles? – Common Reasons & Easy DIY Fixes!


If you notice a rattling sound when driving your car, there’s a high chance the catalytic converter is to blame.

Dig in as we discuss what causes a catalytic converter to rattle, the common signs, the dangers, and how to fix this problem before it ruins your car engine.

Why is My Catalytic Converter Making Rattling Noises?

A catalytic converter resembles a large metal box mounted on the underside of your car. It’s a crucial part of the exhaust system located between the muffler and the engine.

It comprises a stainless steel casing housing a ceramic honeycomb structure lined with catalysts such as palladium, platinum, and rhodium.

Like other car components, the catalytic converter is susceptible to damage and can wear down in time. You’re likely to hear a rattling sound coming from the converter if the internal structure is compromised or damaged.

Common Causes of Catalytic Converter Rattle

If the heat shield is loose and rubbing against the cab floor, you may hear a rattling noise in the catalytic converter. Residue buildup or a damaged honeycomb structure inside a converter are the other two most common causes of this noise.

1. Loose Heat Shield

Catalytic converters generate temperatures exceeding1200°F when the car is under heavy load. The temperatures in a faulty converter can be as high as 2000°F, which is enough to cause extensive damage.

The heat shield, mounted to the underside of your car using nuts and bolts, protects the car and the environment from heat damage. Excessive car vibrations and corrosion may loosen the bolts or cause them to fall off. That allows the now-loose heat shield to rattle against the cab floor when the car runs.

A loose heat shield isn’t a serious issue, but failing to fix the problem may cause the shield to fall off. That may expose your converter to further damage while exposing your cab floor to heat damage.

Rattling noises that intensify when you accelerate strongly indicates you have a bigger problem. It indicates the presence of loose elements in the exhaust system.

2. Residual Build Up

Dirt, debris, carbon, hydrogen sulfide, and other residues often accumulate inside a catalytic converter over time. Leaked oil, overly rich fuel mixtures, subgrade fuel, and burned coolant are common sources of residue buildup in the catalytic converter.

These residues clog the converter and interfere with its normal operations. They lower its efficiency and cause it to make noises such as rattling. When a catalytic converter fails to convert the exhaust gases properly, residues buildup in the catalysts, creating blockages that cause the rattling noise.

3. Damaged Honeycomb Structure

A catalytic converter comprises a ceramic honey structure, which may sustain damage or simply wear out from driving. Damage to the ceramic honeycomb monolith may result from physical impact, excessive engine vibration, or corrosion. The damaged internal system may be responsible for the rattling noises you hear while driving the car.

Damage to the honeycomb structure creates gaps. Exhaust gases escape through the damaged areas, causing the catalytic converter to rattle. The cracked pieces may also produce a rattling noise as they move around inside it.

Excessive heat also causes the honeycomb structure to crack, break or disintegrate into small pieces that rattle around. The broken parts may rattle as they move around the converter and cause severe engine and performance problems. Residue buildup on the catalysts causes blockages that hinder airflow in the converter, causing it to overheat.

Excessive heat damages and melts some converter components. That creates blockages that further clog the system, leading to extensive car engine damage.

Besides rattling, faulty catalytic converters produce other noises, such as pinging, ticking, popping, and knocking.

Other Common Noises from a Faulty Catalytic Converter

A faulty catalytic converter will produce other noises besides a rattle. Each noise often points to a different problem. Telling apart the sounds a bad converter makes can help you identify the specific problem.

  • Ticking noises occur when a converter is burning off oil, fuel, or coolant. You may hear the sound during a cold startup, idling, or acceleration.
  • Pinging noises from a converter may indicate clogging due to age, overheating, or contaminated fuel.
  • Knocking noises in a catalytic converter could indicate a loose heat shield or a leak.
  • Popping converter noises indicate a clog is restricting airflow and causing backpressure.

7 Telltale Signs of a Faulty Catalytic Converter

Besides the rattling sounds, there are other signs that the catalytic converter in your car is failing. A bad catalytic convert may cause your engine to overheat, leading to extensive damages that cost you a fortune to fix. Timely action increases the lifespan of your converter and saves you hundreds of dollars in catalytic converter replacement costs.

Here are 7 common signs that your catalytic converter is going bad:

1. Poor Engine Performance

You’ll notice a significant drop in car performance when the catalytic converter is clogged, leaky, or blocked. Clogging impairs airflow and traps the exhaust gases within the car’s exhaust system. The resultant pressure buildup stops the engine from breathing, lowering its power and degrading its performance.

A failing catalytic converter causes engine stutter on startup and acceleration delays. The engine may struggle and lose power when going uphill or downhill.

Poor engine performance can be downright dangerous and endanger your life. A sudden pressure buildup may cause your engine to stall while tearing down the highway. A faulty catalytic converter may also cause the car to jerk and lose acceleration power while accelerating to pass.

Before taking any corrective measures, you must be sure the catalytic converter is to blame for poor engine performance. Testing the exhaust force and flow eliminates any doubt.

  1. Place the car in park with the engine running.
  2. Have someone rev the engine to about 2,000 rpm.
  3. Place your hand close to the tailpipe.
  4. Feel the amount of heat and heat coming from the exhaust. If the exhaust gases are light, hot, or scanty, your catalytic converter is likely failing.

You may compare the exhaust emission force and amount with a car of a similar make and model.

2. Increased Fuel Consumption

Are you spending more money on gas than usual lately? If you notice a sudden spike in your fuel consumption, a faulty catalytic converter may be to blame. Declining fuel efficiency is indicative of a failing catalytic converter.

Cars with damaged catalytic converters are thirsty. Poor airflow lowers fuel-burning efficiency causing them to consume more fuel.

You may have trouble starting your car when the converter is faulty. Excess fuel often gets into the combustion chamber and floods the engine. The engine may ignite but stall within seconds. It’ll sputter and die because the gases can’t escape from the combustion chamber quickly enough.

The excess fuel may cause the exhaust gases to ignite in the exhaust system. That causes a sudden pressure buildup that stalls the engine while the car moves.

3. Rattling Noise

Rattling noises under your feet while driving is another crucial symptom of a faulty catalytic converter. With time and usage, residuals from leaking coolant, oil, or rich fuel mixture may coat the ceramic honeycomb monolith.

The residuals may clog or cause the ceramic to crack, break, and disintegrate into pieces. The fragments from the broken ceramic honeycomb are the culprits behind the rattling noises.

Initially, the rattling noise is more noticeable when starting the engine. The rattling gets louder as the problem persists, and the noise can be heard when the car is idling or accelerating.

4. Rotten Egg Smell

A distinct exhaust smell spells trouble. Regular exhaust gas is unremarkable – it has a smoky and musty odor. If your car produces exhaust gases with a distinct noxious smell reminiscent of rotten eggs, sewer gas, or sulfur, your catalytic converter may be damaged.

A fully functional cat converts hydrogen sulfide, the gas responsible for the rotten egg smell, into odorless sulfur dioxide. If your car’s exhaust smells like brimstone, the converter is compromised and isn’t doing its job.

Besides the noxious odor, you may notice the exhaust is darker. The exhaust from an efficient converter is odorless and colorless.

5. An Illuminated Check Engine Light

Newer car models feature sensors that monitor the catalytic converter’s efficiency and the gas levels in the exhaust system. The oxygen sensors alert the car’s computer if the converter isn’t properly catalyzing the exhaust or is operating sub-optimally. The car’s computer will turn on the check engine light to alert you of the issue.

However, an illuminated check engine light is not a definitive indicator of a bad catalytic converter. The light alerts you to an issue with your engine but doesn’t tell you the exact problem.

Scanning the car with a diagnostic scan tool is the best way to retrieve the actual trouble codes. Trouble codes P0420 and P0430 indicate your car has a catalytic converter problem.

6. A Misfiring Engine

A damaged catalytic converter leads to fuel misfires, distinct from other types of misfires. Typically, your engine is likely to misfire when there’s incomplete combustion and one or more cylinders remain unfired.

A clogged converter limits the amount of fuel reaching the ignition cylinder and causes the car to misfire. Clogging restricts airflow, denying the engine the oxygen it needs for proper fuel combustion.

Residuals from improper combustion may coat the sparkplugs and cause them to misfire. Restricting the airflow may also heat the exhaust gases and cause them to ignite without input from the sparkplugs, causing a misfire.

Using an overly rich fuel mixture may also cause a misfire. Raw fuel may ignite inside the catalytic converter and cause it to overheat. The excess heat may melt some of the converter’s components and damage the car’s exhaust system.

7. Failed Emission Test

Inefficiency occurs when a catalytic converter is clogged, damaged, or leaky. There’s an unusual darkening and increased exhaust volume when the converter fails. Your car is likely to fail an emission test if you live in a state that conducts emissions if the catalytic converter is faulty.

The diagnostics during an emissions test will betray you if the oxygen sensors or a converter failure has ever triggered the check engine light. The EMC stores all the data from the oxygen sensors. Have an automotive specialist inspect and fix the problem. You’ll need the maintenance report to pass the pollution test.

How to Fix a Rattling Catalytic Converter

A rattling catalytic converter is a warning sign. It’s an unmistakable indicator of a severe underlying problem with your car. The rattling noises often result from a loose heat shield, dirt buildup in the ceramic honeycomb, or a fractured monolith. You can quickly fix the rattle in your catalytic converter regardless of the cause.

6 Simple Ways to Quiet a Rattling Catalytic Converter

1. Switch to High Octane Fuel

You’re likely to have carbon or a residual buildup in the engine if you usually drive your car over short distances. See, catalytic converters perform optimally over a specific temperature range. Short commutes don’t raise the engine and cat temperature to the required levels.

Long drives make your engine work harder and raise the temperatures. If your car engine runs hot regularly, you’re unlikely to have a problem with carbon buildup. Tearing down the highway at high speeds (within the speed limits) for several hours a month is good preventive maintenance practice. It can help you burn off any buildup in the catalytic converter.

Switching to high-octane gas can help prevent residual buildup in the converter. High-octane fuel is pricier than regular gas but significantly cheaper than a new converter.

Besides, you only need to fill your tank with expensive gas every third or fourth tank of gas. Some fuels contain additives designed to unclog and remove buildups in car engines and converters.

Switching to high-octane fuel every so often safeguards your car engine. The better fuel can dissolve the carbon buildup and unclog your converter. It may also improve mileage and eliminate other engine noises.

2. Tighten the Heat Shield

Catalytic converters generate a lot of heat. The typical operating temperatures in a converter are 500 to 800°Fbutwill spike to 1200°F when hauling heavy loads.

A catalytic heat shield protects the surrounding ground cover and the cab floor from heat damage. The temperatures in a clogged converter can skyrocket to 2000°F, which is enough to melt its components.

Rattling noises are noticeable if the heat shield becomes loose and bangs on the cab floor. Sometimes stones and pebbles become trapped between the shield and its stainless-steel housing, creating quite a ruckus. Tightening or replacing the bolts solves this problem.

  1. Loosen the bolts with penetrating oil.
  2. Remove all the bolts and detach the heat shield. Be careful not to damage the metal flanges.
  3. Wash the converter’s body and the heat shield to keep them clean and reflective. You may use high-grit sandpaper to give the metal an extra shine. A bluish tinge on the shield and converter housing indicates excessive heating. It could be a sign of blockage within the converter’s chambers.
  4. Replace the faulty bolts and reattach the heat shield securely to its housing. It’s advisable to use anti-seize on the bolts.

If the welded bolt flanges are damaged, you may use a galvanized strap clamp to fasten the heat shield. Alternatively, consider finding a replacement heat shield.

3. Clean it with a Lacquer Thinner

A rattle accompanied by decreasing fuel efficiency and engine performance often indicates a residual buildup in the converter. Adding lacquer thinner to the fuel tank is a quick and easy way to fix a rattling converter.

  1. Wait until the gas tank is almost empty.
  2. Add a gallon of lacquer thinner into the tank.
  3. Top up your gas tank with 10 gallons of gasoline.
  4. Head to the nearest highway and drive for about 150 miles. The trip should take you about 2½ hours.
  5. Get the engine working at 2,500 rpm or more for 30 to 40 minutes (50 to 70 miles) during the trip.

The sustained, high-temperature engine workout will burn off the residue blockage clogging the engine and converter. You’ll notice an immediate improvement in fuel efficiency and engine performance.

The rattle should also disappear. If the rattle persists, you could be dealing with much more than a residual blockage. Your catalytic converter may be cracked, or the ceramic monolith could be broken.

4. Use Cataclean Fuel and Exhaust Cleaner

Cataclean Fuel and Exhaust Cleaner is the ultimate grease stripper for car engines. The EPA-approved cleaner removes residues and carbon buildups in catalytic converters, cylinder heads, oxygen sensors, fuel injectors, and tappets.

  1. Ensure you have about 4 gallons of fuel in your tank.
  2. Empty a 16 oz Cataclean bottle into the fuel tank.
  3. Drive your car for at least 15 minutes to let the cleaner into the converter and engine.
  4. Clear the Check Engine light if it’s still illuminated after your drive.
  5. Fill the tank with fresh gas (or at least ¾ tank) and take a long driveof at least 50 miles.

You should notice perked engine performance and improved fuel efficiency after using Cataclean. Any rattle caused by residue blockage should disappear as well. Using Cataclean every three months protects your catalytic converter from carbon buildup clogging.

5. Clean Your Catalytic Converter with Sodium Hydroxide

Faulty catalytic converters often fail to convert hydrogen sulfide into odorless sulfur dioxide. This gives your car’s exhaust a characteristic rotten egg smell. With time the hydrogen sulfide residue may build up and clog the converter chambers and cause a rattle.

Cleaning your converter with sodium hydroxide eliminates the hydrogen sulfide residue. However, this isn’t a simple cleaning process. You’ll need to detach the cat from the car before you can clean it with sodium hydroxide.

  1. Hoist the car and remove the catalytic converter.
  2. Pour the sodium hydroxide into a spray bottle.
  3. Squirt generous amounts of the cleaning solution into both ends of the converter. Coat the honeycomb structure generously.
  4. Leave the sodium hydroxide to soak for 20 to 30 minutes.
  5. Rinse the converter thoroughly with clean water. Hose it down until the water runs clean.
  6. Reinstall the converter and secure it firmly to the car.

You’ll notice a remarkable improvement in engine performance, and the converter rattle will be gone.

6. Repair the Faulty Parts

Typically, repairing a faulty converter entail replacing the defective parts with new ones. Repairing a catalytic converter can be an affordable way to fix a rattling noise.

Yet despite popular opinion, some parts, such as honeycomb monoliths, aren’t repairable. If the unit is extensively damaged, you may need to replace it.

7. Replace Your Catalytic Converter

Catalytic converters are meant to last the lifespan of your vehicle but usually won’t due to wear and tear. Most converters start failing after 70,000 to 100,000 miles.

The cost of catalytic converter replacement ranges between $800 and $2200. The cost varies wildly between car makes and models, but you must dig deeper into your pockets if you drive a car with a large engine.

You may keep the replacement costs low and affordable if you’re handy with a wrench and know how to fit a new catalytic converter.

How to Replace a Rattling Catalytic Converter

The exorbitant catalytic converter replacement costs may have you wondering if you can replace the converter on your own. Luckily, replacing a converter isn’t complicated. You can easily get it done if you purchase the correct converter for your vehicle.

Unless you’re a skilled welder, be sure to purchase an OEM converter – one designed for your car’s make and model – not a universal fit. A Direct-Fit converter uses nuts and bolts, while a universal cat requires welding.

18 Steps to Replace a Catalytic Converter

  1. Raise the car off the ground and mount it on jack stands.
  2. Douse the nuts and bolts on the cat and the threads of the oxygen sensors with penetrating oil. Leave them to soak for 4 to 12 hours.
  3. Wear safety glasses and slide underneath the car.
  4. Detach the cables running from the oxygen sensors and disconnect the oxygen sensors.
  5. Unfasten the bolts anchoring the heat shield, then remove the shield.
  6. Secure the converter so it doesn’t fall. A catalytic converter is heavy, and it might drop on the floor and sustain damage or injure your head.
  7. Loosen the bolts, clamps, hangers, and fasteners securing the converter to the car.
  8. Disconnect the gasket flanges. Gently pry the gasket flanges open and remove the gasket with the converter. You may need to cut the gasket flanges free if they’re welded in place.
  9. Clean the gasket surfaces and connecting flanges.
  10. Install the replacement catalytic converter
  11. Douse the oxygen sensor threads with anti-seize and fasten them with a wrench.
  12. Set the gasket into the flange between the converter and the manifold. Then secure the connection bolts. Be sure to support the converter to avoid damage.
  13. Repeat the gasket placement process on the tail end of the catalytic converter.
  14. Install the heat shield and tighten the bolts with a wrench.
  15. Reconnect oxygen sensor wires and lower the car to the ground.
  16. Reset the diagnostic error codes, switch on the engine, and let the car idle for a while.
  17. Rev the engine to reach the normal operating temperature. Leave the car to idle for 5 minutes, then raise the rpm to 2500 for 2 minutes.
  18. Shut off the engine and leave the engine to cool

Replacing the converter will most definitely eliminate the noise!

How to Remove and Clean a Rattling Catalytic Converter

You only need access to the vehicle’s underbody to remove and clean the converter.

Ideally, you should clean the catalytic converter over the weekend because the process takes time, and the exhaust system must be cool to the touch.

  1. Hoist the car using a jack and secure it on the jack stands.
  2. Spray the front and rear bolts on the catalytic converter with WD-40 and leave them to soak overnight.
  3. Remove the catalytic converter. Use a long socket arm to unscrew the bolts and standard wrench on the nut. You’ll need plenty of elbow grease to loosen the bolts.
  4. Give the converter a thorough shake. If you notice any rattling sound, the honeycomb structure is broken. You may need a replacement catalytic converter.
  5. Hold the converter upright and spray its interior with brake cleaner fluid. Leave the cleaner to soak, then shake it out the dislodged residue. Flip the converter and repeat the process on the other side.
  6. Leave the freshly cleaned converter to dry.
  7. Reinstall the clean catalytic converter and bolt it securely under your car.

How Much Does It Cost to Replace a Catalytic Converter?

The cost you’ll incur when replacing a catalytic converter depends on whether it’s a two- or three-way converter. It also depends on the size, year, make, and model of your car.

Your choice of a converter – OEM or universal fit – and installation mode also affect the overall price. Hiring a professional for the job adds $100 to $300 to the converter installation costs.

State requirements also affect the cost of converter replacement and installation. Converter replacements may need to adhere to the California Air Resource Board (CARB) or Federal EAP emissions standards.

An OEM, also known as a Direct-Fit, is easier to install because it’s specific to the year, make, and model of your car. However, OEM catalytic converters are more expensive.

Universal catalytic converters are affordable generic models made by third-party manufacturers. They don’t conform to conventional standards and are more tedious to install.

Many auto parts resellers stock used OEM catalytic converters. Recycled converters make a great choice if you’re on a tight budget. Inspect the part and only purchase one from a reliable dealer.

Catalytic Converter Replacement Costs

Catalytic converter replacement costs range from $500 to $2,200. The cost of purchasing a converter depends on the type of converter, your car’s YOM, make, and model.

A Direct-Fit catalytic converter will cost more than a universal fit, but it’s easier to install. A professional installation may add up to $300 in labor charges to the installation costs.

You can lower the price by installing the converter yourself if you have the time, tools, and the right materials.

Is It Safe to Drive with a Rattling Catalytic Converter?

Driving with a rattling converter is mostly safe but not advisable. For starters, it’s terrible for the environment and may damage your converter further.

If the rattling results from residual buildup in the converter, driving the car may not damage your engine. However, it may mean your vehicle will fail the emission test, which could saddle you with huge fines. A failed pollution control test may render your vehicle undrivable in some jurisdictions until you fix the problem.

It’s technically safe to drive the car if a loose heat shield is causing the rattling. However, fixing the problem is best to prevent the guard from falling off, which could lead to extensive car damage.

You may safely drive a car with a damaged honeycomb structure, but it’s not safe for the environment. Your vehicle has higher emission levels and will undoubtedly fail an emission test.

Driving a car with a blocked catalytic converter invites serious trouble. The blockage generates backpressure, which causes the engine to run rough and lose power and performance. The backpressure may cause the car to stall, backfire, and have trouble starting. Left unattended, a blocked converter could lead to costly engine damage.

Maintenance Tips to Keep Your Catalytic Converter Healthy

The typical lifespan of a catalytic converter is about 10 years, 100,000 miles, or last as long as the car. However, how long your catalytic converter lasts depends on your driving habits, fuel choice, maintenance routine, and the environment. Proper maintenance and careful driving can help you maximize the lifespan of your catalytic converter.

Here are 10 proven ways to give your catalytic converter a long, healthy life:

  1. Never use exhaust paste when fitting a catalytic converter. After hardening, the paste can break into pieces that can damage the honeycomb monolith.
  2. Always top up your car with quality fuel and oil
  3. Pick your fuel additives carefully. Read the instructions to ascertain whether the additives suit your catalytic converter.
  4. Refrain from tow-starting your car. A bump start forces unburned fuel into the catalytic converter and may cause the honeycomb monolith to overheat and melt.
  5. Never exceed your vehicle’s towing capacity. An excessively heavy tow load pushes your car along when traveling downhill, sending unburned fuel into your exhaust system.
  6. Follow the manufacturer-recommended service plan. Regular servicing keeps your engine running smoothly and prevents residue buildup that might damage the monolith.
  7. Avoid driving through deep puddles on parking in deep snow. Catalytic converters operate at high temperatures. They’re forced to cool down rapidly when you drive through water or snow. Since the stainless steel housing is a good conductor of heat, it cools faster than the ceramic monolith. In extreme cases, the contracting steel shell may crush the honeycomb monolith.
  8. Avoid parking your car on long grass or dry vegetation. A hot heat shield may set the material on fire and damage your car.
  9. Drive carefully on bumpy roads and over speed bumps. Running over obstacles on the road increases the chances of grounding your exhaust system. The impact may cause severe damage to your catalytic converter.
  • Never ignore the warning lights on the dashboard. Investigate an illuminated check engine light as soon as it appears. It’s your chance to fix a catalytic converter problem before it compounds.

FAQs

Can you fix a rattling catalytic converter?

You can fix a rattling catalytic converter by tightening a loose heat shield or cleaning it with brake fluid, sodium hydroxide, Cataclean, or lacquer thinner. Cataclean and lacquer thinner are the easiest way to fix a converter rattle since you don’t need to remove the converter from the car. You may need to replace the converter if it’s sustained extensive physical damage.

What does a faulty catalytic converter sound like?

A faulty catalytic converter produces a variety of noises, including rattling, popping, knocking, pinging, and popping. Each type of noise points to a different kind of converter issue.

How much does a professional catalytic converter installation cost?

A professional installation takes about two hours and will set you back $800 to $2,200. A DIY converter installation may save up to $300 in labor charges. You can easily replace a catalytic converter if you have the time, tools, and necessary parts.

How do you fix a rattling catalytic converter shield?

You can fix a rattling catalytic converter shield by removing any stones trapped inside and tightening the loose bolts. You’ll need to replace lost, damaged, or corroded bolts while fastening the shield.

How much does it cost to fix the catalytic converter?

The cost of fixing a catalytic converter range from $200 to $2,200. The overall cost depends on whether the converter is clogged or damaged. Carbon buildups and other residues are cheaper to fix, while physical damage may require you to buy a new converter, driving up the costs.

Keep Your Catalytic Converter in Great Shape

A rattling noise in your catalytic converter indicates a problem with your exhaust system. Taking quick corrective action lets you nip the problem in the bud and extend the lifespan of your converter.

You can fix a catalytic converter rattle by either tightening the loose heat shield, cleaning or replacing the converter depending on the source of the issue.

Hopefully my tips will help you identify the cause and resolve it without having to pay a professional mechanic a hefty sum!

Peter Bone

Soundproof expert and a staunch opponent of noise. This website is a free source of information on how to 'keep it down a notch'. I update the content regularly to keep up with advancements in the soundproofing industry.

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