Can You Still Drive If Your Catalytic Converter Is Bad?

Usually yes, your car will run and you can drive a short distance with a bad catalytic converter, but it’s risky and often illegal to ignore: performance may drop, emissions rise, parts can overheat, and you could fail inspections. If the converter is severely clogged, the engine may stall or struggle to accelerate—at that point, stop driving and have the car towed. Below is what that means in practice, how to tell what’s safe, and what to do next.

What the Catalytic Converter Does—and Why It Matters

The catalytic converter turns harmful exhaust gases—carbon monoxide, hydrocarbons, and nitrogen oxides—into less harmful emissions. Modern vehicles rely on it, along with oxygen sensors and engine controls, to meet emissions standards and protect public health. When it fails, damage can cascade through the exhaust and engine, and you can run afoul of emissions laws and inspection rules.

What “Bad” Looks Like: Common Symptoms

Drivers often first notice warning signs before the converter completely fails. The following symptoms are among the most frequent:

• Check-engine light with codes like P0420 or P0430 (catalyst efficiency below threshold).
• Noticeably reduced power, especially under load or at highway speeds.
• Poor fuel economy and rough running; in severe cases, stalling after a few minutes.
• Rotten-egg or sulfur smell from the exhaust (from hydrogen sulfide).
• Rattling noises under the car (loose substrate inside the converter).
• Exhaust components or the converter glowing red from excessive heat.

Any one of these signs warrants prompt diagnosis; a combination—especially power loss, overheating, or strong odors—suggests the problem is advanced.

Can You Keep Driving? It Depends on the Failure

When Limited Driving May Be Possible

In some scenarios, short, low-load trips to a repair shop are typically acceptable. Consider the following as “limp to service” situations:

• The car runs normally apart from an illuminated check-engine light and a P0420/P0430 code.
• No severe power loss, no overheating, and no strong exhaust smells in or around the cabin.
• No rattling from the converter and no signs of exhaust leaks.
• You’re driving only a short distance directly to diagnosis or repair.

Even then, avoid hard acceleration and extended highway climbs, and schedule repair quickly to prevent damage and legal issues.

Stop Driving and Arrange a Tow If You Notice

Other conditions indicate immediate risk to the vehicle or your safety. If you encounter any of the following, do not continue driving:

• Severe loss of power, bucking, or stalling—signs of a clogged converter.
• Engine overheating, a glowing-red converter, or burning smells.
• Active misfire or rough running (a misfire can quickly destroy a converter).
• Strong sulfur or exhaust fumes, especially in the cabin.
• Rattling from the converter (broken substrate that can migrate and clog).
• Exhaust leaks or extremely loud exhaust (common if the converter was stolen).

Continuing to drive under these conditions can damage the engine and exhaust system and increases fire and fume risks.

Risks of Continuing to Drive With a Bad Converter

Driving far with a failing catalytic converter isn’t just an emissions problem—there are practical and legal consequences too:

• Engine damage: Excess backpressure can overheat valves and the exhaust manifold; raw fuel from misfires can melt the converter and O2 sensors.
• Performance and economy: Power loss and poor fuel economy often worsen over time.
• Safety: Overheated exhaust components can pose a fire risk; leaks can allow fumes into the cabin.
• Legal and inspection failures: You’re likely to fail emissions/inspection, blocking registration in many areas.
• Higher repair costs: Ignoring root causes (misfires, oil burning, coolant leaks) can destroy a new converter.
• Warranty considerations (U.S.): Federal emissions warranty covers the catalytic converter for 8 years/80,000 miles on new vehicles; beyond that, you pay out-of-pocket.

In short, “it still drives” can quickly become “it won’t start” or “the repair just got a lot more expensive.”

Legal and Inspection Considerations

In the U.S., the Clean Air Act prohibits tampering with emissions systems; driving without a converter (after theft or removal) is illegal and will fail inspection. Even a degraded converter can trigger a check-engine light and readiness-monitor failure, causing an inspection or registration denial. Some states—California, Colorado, Maine, and New York—require CARB-compliant aftermarket converters, which are pricier but mandatory. In the U.K. and EU, a faulty or missing converter typically fails MOT/roadworthiness tests, and driving an unroadworthy vehicle can lead to fines and invalidated insurance. Always check local regulations before operating the vehicle.

What to Do Next: Diagnosis and Repair

To minimize cost and prevent repeat failures, take a systematic approach to diagnosis and replacement:

1. Scan for OBD-II codes and fuel trims to confirm catalyst efficiency faults and look for root causes (misfires, rich/lean conditions).
2. Fix the cause first: Address misfires (plugs, coils, injectors), vacuum leaks, coolant or oil consumption, and sensor issues before replacing the converter.
3. Confirm restriction: A backpressure test or upstream/downstream O2 patterns can reveal a clogged converter; a non-contact thermometer can spot hot spots.
4. Inspect physically: Look for exhaust leaks, rattling substrate, or impact damage from road debris; check heat shields and hangers.
5. Select the right part: Use OEM or, where required, CARB-compliant converters; match the exact engine and chassis configuration.
6. Consider theft coverage: If stolen, file a police report and an insurance claim; many comprehensive policies cover converters, O2 sensors, and pipe repairs.
7. Protect the replacement: After repair, verify no misfires, reset monitors, and avoid extended idling or short-trip cycles while monitors relearn.

This sequence helps ensure you replace the converter only once and restore emissions compliance quickly.

Costs and Timing

Costs vary by vehicle and location. Aftermarket non-CARB converters for many mainstream cars often run $300–$1,200 plus $150–$400 labor. OEM units, turbo or high-performance systems, and multi-converter setups can range from $800 to $2,500+ per converter. In CARB states, compliant aftermarket parts typically cost $1,000–$3,000 installed. Theft-related repairs can be higher due to collateral damage and sensor replacement. Parts availability is generally good in 2025, but popular models targeted for theft can see occasional delays.

Prevention and Longevity

Good maintenance habits dramatically extend converter life and reduce the chance of a repeat failure:

• Address check-engine lights and misfires immediately.
• Fix oil or coolant consumption that contaminates the catalyst.
• Use the correct fuel and avoid lead or unapproved additives.
• Keep the ignition and fuel systems in spec (plugs, coils, injectors, sensors).
• Warm the engine fully on longer drives so the catalyst reaches efficient operating temperature.
• Install anti-theft shields or secure parking if theft is a risk for your model.

These steps help the converter operate at the right temperature and chemistry, preserving performance and emissions compliance.

Bottom Line

You can often drive briefly with a bad catalytic converter, but it’s unwise and sometimes unlawful to defer repair. If the car still runs normally, go directly to a shop; if there’s power loss, overheating, strong odors, or misfiring, stop and tow. Fix underlying engine issues first, then replace the converter with the correct compliant part to restore reliability and pass inspection.

Summary: Limited short-distance driving may be possible with mild symptoms, but advanced failures pose safety, legal, and cost risks. Diagnose promptly, address root causes, and use the right replacement to avoid repeat problems.

How long can you drive without replacing a catalytic converter?

You should replace your catalytic converter as soon as possible if it is failing, as a completely failed converter can damage your engine and cause a severe power loss. While a converter can last many years, a faulty unit poses risks to your car and the environment, and you should not continue to drive with a bad converter indefinitely. 
Why you shouldn’t delay replacement

• Engine damage: A clogged catalytic converter can cause serious engine failure over time. 
• Performance loss: You will experience reduced engine power and poor fuel efficiency. 
• Legal issues: Driving without a functioning catalytic converter is illegal in many places due to its role in reducing harmful emissions. 
• Emissions failure: You’ll likely fail an emissions test. 

Signs of a failing catalytic converter 

• A check engine light or a P0420 error code.
• A sulfur (rotten egg) smell from the exhaust.
• Reduced engine performance or difficulty accelerating.
• A rattling sound from under the vehicle.

What to do next

• Get it diagnosed immediately: Visit a qualified mechanic to have the catalytic converter inspected. 
• Don’t wait: If the converter is damaged, failing, or clogged, it needs to be replaced without delay to prevent further issues. 

How much does it cost to fix a catalytic converter?

Replacing a catalytic converter can cost anywhere from $300 to over $2,500, with the average price often falling between $1,000 and $2,500 for direct-fit replacements, including parts and labor. Costs vary significantly based on the vehicle’s make and model, the type of converter (direct-fit vs. universal or aftermarket), the presence of precious metals, and the labor rates of the mechanic. 
Factors influencing the cost:

• Vehicle Type: Economy cars like a Honda Civic typically have lower costs, while luxury vehicles or those with more complex exhaust systems (like trucks and SUVs) require more expensive parts. 
• Type of Catalytic Converter:
  • Universal Converters: These are cheaper and can be welded onto the exhaust system, potentially costing around $300 for a simple replacement. 
  • Direct-Fit Converters: These are designed for specific vehicles and include portions of the exhaust pipe, leading to higher prices, often $2,500 or more. 
  • Original Equipment Manufacturer (OEM) vs. Aftermarket: Dealerships often use more expensive OEM parts, while independent shops may offer more affordable aftermarket options. 
• Precious Metals: Catalytic converters contain precious metals like platinum, palladium, and rhodium. The fluctuating prices of these metals influence the cost of the part. 
• Labor Costs: Shops charge for labor, which can vary depending on the complexity of the installation and the mechanic’s hourly rate. 
• Location and Damage: If the catalytic converter was stolen, the repair will include parts and labor. If the converter is also a component of the exhaust manifold, more time and effort may be needed to gain access for replacement. 

Tips for saving money:

• Get Quotes from Multiple Shops: Opens in new tabCompare prices from different mechanics, including independent muffler shops, to find the best value. 
• Consider Aftermarket Parts: Opens in new tabAftermarket or universal converters are often more affordable than OEM parts. 
• Check for Damage: Opens in new tabInspect the surrounding area for any additional damage that might increase repair costs beyond the catalytic converter itself. 

How does a car act when the catalytic converter is going out?

Symptoms of a bad catalytic converter include a rotten egg or sulfur smell, reduced engine power and poor acceleration, a rattling noise from under the car, a lit check engine light, decreased fuel economy, engine misfires, and a failure to pass an emissions test. A completely clogged converter can even lead to the engine stalling. 
Common Symptoms

• Sulfur or Rotten Egg Smell: Opens in new tabThis is a key indicator that the converter isn’t effectively converting hydrogen sulfide into a harmless gas, causing that distinct smell to emanate from your exhaust. 
• Reduced Engine Performance: Opens in new tabA clogged converter restricts the flow of exhaust gases, making your engine work harder and resulting in decreased acceleration and power. 
• Rattling Noise: Opens in new tabIf the internal components of the converter have broken loose, you might hear a rattling sound coming from underneath your vehicle, especially when the engine is starting or under load. 
• Check Engine Light: Opens in new tabYour vehicle’s computer will often detect the issue with the catalytic converter’s performance and illuminate the check engine light. 
• Engine Misfires: Opens in new tabA clogged converter can cause pressure buildup that leads to engine misfires, which can be a serious issue for engine components. 
• Decreased Fuel Economy: Opens in new tabThe engine having to work harder to push out exhaust gases causes it to burn more fuel, leading to noticeably lower gas mileage. 

Less Common or More Severe Symptoms

• Dark Exhaust Smoke: Opens in new tabA functioning catalytic converter breaks down harmful particles; if the fumes are dark, it suggests the converter isn’t doing its job. 
• Engine Overheating: Opens in new tabThe engine can run hotter due to restricted exhaust flow and increased internal pressure. 
• Vehicle Stalling: Opens in new tabIn cases of a severe clog, the exhaust pressure buildup can be so significant that it causes the engine to stall. 

What happens if you drive with a bad catalytic converter?

Driving with a bad catalytic converter leads to significantly increased vehicle emissions, reduced engine performance (power loss, poor acceleration, and decreased fuel economy), a check engine light, and potential engine damage. A seriously clogged converter can cause catastrophic engine damage from back pressure and even a dangerous vehicle fire by trapping exhaust heat. 
Environmental & Legal Consequences

• Increased Emissions: A failing converter cannot reduce harmful pollutants, leading to higher levels of harmful gases in the atmosphere. 
• Failed Emissions Test: Your vehicle will likely fail a mandatory emissions inspection in most areas. 

Performance Problems

• Power Loss & Poor Acceleration: Opens in new tabAn obstructed converter restricts exhaust flow, preventing the engine from “breathing” efficiently, resulting in reduced power and sluggish acceleration. 
• Decreased Fuel Economy: Opens in new tabThe engine has to work harder to overcome the back pressure, which leads to worse gas mileage. 
• Engine Misfires & Rough Idle: Opens in new tabThe incomplete combustion caused by the restricted exhaust can lead to engine misfires, a rough idle, and difficulty starting the car. 

Safety & Damage Risks

• Vehicle Fire Risk: Opens in new tabA clogged converter can become extremely hot due to trapped heat, posing a serious fire risk to the vehicle. 
• Engine Damage: Opens in new tabProlonged driving with a clogged converter can create excessive back pressure that damages engine components like pistons, rings, and bearings. 
• Exhaust Leaks into Cabin: Opens in new tabA broken or deteriorated converter could allow toxic exhaust gases to leak into the vehicle’s cabin, creating a deadly health hazard. 

What to Do

• Get Professional Diagnosis: Opens in new tabIf you suspect a bad catalytic converter, have it professionally diagnosed. 
• Address Symptoms Promptly: Opens in new tabDon’t delay repairs, as the issue can lead to more severe and expensive damage.