How do I know if my catalytic converter was stolen?

Quick answer: if you hear a very loud exhaust, notice a visible gap or missing exhaust section where the converter should sit, or the check engine light comes on with codes such as P0420 or P0430, your catalytic converter could have been stolen. Thefts have risen in many areas due to the valuable metals inside. Thieves typically cut the converter from the exhaust and take it away, leaving an opening under the vehicle. This article explains how to recognize the signs, the steps to take if it happened, and practical ways to reduce the risk in the future.

Identifying the signs of a stolen catalytic converter

Visual and auditory clues

Look under the vehicle for a missing or damaged exhaust segment between the downpipe and the muffler, and listen for unusual sounds that weren’t there before. A thief will typically leave a large gap where the converter sat, often with sharp-edged cut marks on surrounding metal.

• Visible gaps or a missing catalytic converter under the car, often with cut pipes.


• Very loud exhaust noise — a deep rumble or roaring sound, especially when you accelerate.


• Metallic rattling or vibrations from the undercarriage, particularly shortly after starting or at idle.


• Signs of tampering near the exhaust area, such as fresh metal shavings or cut heat shields.

If you notice these signs, avoid prolonged driving and have your vehicle inspected by a professional as soon as it’s safe to do so.

Diagnostics and vehicle codes

After removing the converter, the engine’s sensors may trigger fault codes or illuminate the check engine light. The most common catalytic converter-related codes are P0420 (Catalyst System Efficiency Below Threshold) and P0430 (Catalyst System Efficiency Below Threshold for Bank 2). A scan tool can read these codes and help verify a catalyst issue versus a sensor fault.

What to do if you suspect your catalytic converter was stolen

If you suspect theft, treat the situation as urgent safety and legal matter. Follow these steps to document the incident, seek help, and begin replacement.

1. Move to a safe location, if possible, and avoid driving long distances until the vehicle is inspected. If needed, call roadside assistance.


2. Take photos and notes of the undercarriage, the area around the exhaust, and any damage or missing parts. Photograph the missing converter’s mounting area and heat shields.


3. File a police report with as much detail as you can (time, location, any suspects or witnesses). A police report helps with insurance and theft-tracking efforts.


4. Contact your auto insurer to report the theft and start a claim. Some policies cover theft of personal property and vehicle components; coverage varies by policy and region.


5. Have your vehicle inspected by a mechanic or dealership for replacement options, emissions compliance, and proper installation of a new catalytic converter. Expect increased repair costs and potential emissions testing requirements.

Note: Do not attempt to drive the car long distances with the converter missing. Driving without a converter can damage exhaust components and trigger emissions failures, and in many places it may be illegal to operate a vehicle in that condition.

Prevention and minimum-risk steps to protect your catalytic converter

Some protections can reduce the likelihood of theft. Consider combining several methods to increase odds of keeping your converter secure.

• Install a catalytic converter shield or cage and use locking, tamper-resistant bolts or straps to deter quick theft attempts.


• Engrave or register the vehicle’s VIN and a contact number on the converter, and keep photos of the area for police reports.


• Park in well-lit, high-traffic areas or garages when possible. If you can’t, consider camera monitoring around parking areas and near the vehicle.


• Discuss aftermarket protective devices with a reputable mechanic. Some devices are designed to be welded or bolted in place for durability.


• Schedule regular vehicle inspections and emissions checks, especially if you’ve recently had or suspect converter issues.

Implementing multiple layers of protection increases the chances of deterrence and helps with quick recovery if theft occurs.

Summary: The best way to know if your catalytic converter was stolen is to look for a missing converter, listen for a loud exhaust, and check for check engine light with catalytic codes (P0420/P0430). If you suspect theft, stop driving safely, document the scene, report to police, contact your insurer, and arrange professional replacement. Preventive steps such as shields, locking hardware, VIN marking, and secure parking can reduce risk in the future.

How do I know if my catalytic convertor is stolen?

You can tell if your catalytic converter was stolen by a very loud roaring sound when you start your car, a lack of acceleration power, and visual signs of damage or missing parts under your vehicle. Other indicators include a strong exhaust smell inside the car, a check engine light, or failed emissions tests. 
Audio and performance clues 
This video explains the sounds you may hear if your catalytic converter is stolen: 1mThe Enthusiast MechanicYouTube · Jun 5, 2024

• Loud roaring noise: A missing catalytic converter will cause your exhaust to be extremely loud, especially when you start the car or press the gas pedal, as if your car has no muffler. 
• Sputtering acceleration: Your vehicle may feel sluggish, sputter, or have less power than usual. 
• Rough idling: The engine may run unevenly or misfire. 
• Unusual exhaust smell: You may notice strong, noxious, or gasoline-like fumes entering the cabin. 

Visual clues

• Look under the vehicle: Check the area under your car, near the middle of the exhaust system. You will likely see a large gap where the converter was, signs of fresh cuts on pipes, or metal shavings.
• Look for damage: There may be visible damage, such as dents or unusual marks, on the undercarriage or exhaust pipes.
• Missing components: A missing section of pipe or cut wires where an oxygen sensor was connected can also be a sign. 

Warning lights and other indicators
This video demonstrates what a catalytic converter looks like and where it's located under a car: 50s1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · Aug 24, 2024

• Check Engine light: The "check engine" light on your dashboard will likely turn on because the vehicle's computer detects the missing component. 
• Failed emissions test: If your vehicle fails an emissions test, a missing catalytic converter is a likely reason. 
• Health issues: In rare cases, some people have reported headaches or other illnesses due to exposure to exhaust fumes in a poorly ventilated area, as noted on this Allstate article.

Will a car run if the catalytic converter is stolen?

If your catalytic converter has been stolen or you bypass it because it's been having problems, your vehicle will still work. However, without a converter, your car lets out harmful emissions, including carbon monoxide and nitrogen oxides.

How can I check my catalytic converter?

You can test a catalytic converter using an infrared thermometer to check if the outlet is significantly hotter than the inlet, an OBD2 scanner to read diagnostic trouble codes, or a vacuum gauge to measure exhaust back pressure. A clogged or failing converter may also make a rattling sound, or loosening the exhaust pipe can cause a sudden improvement in engine performance. 
Infrared thermometer test
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1. Warm up the vehicle by driving for at least 15-20 minutes to ensure the catalytic converter is hot. 
2. Using an infrared thermometer, measure the temperature at the inlet (front) of the converter. 
3. Measure the temperature at the outlet (back) of the converter. 
4. A healthy converter should have an outlet temperature that is at least 50°F to 150°F hotter than the inlet temperature. 
5. If the outlet is not significantly hotter, or is cooler, the converter may be failing. 

You can watch this video to learn how to use an infrared thermometer to test a catalytic converter: 54smr diyguy123YouTube · Oct 4, 2023
OBD2 scanner test 

1. Connect an OBD2 scanner to your vehicle's diagnostic port. 
2. Look for any diagnostic trouble codes related to the catalytic converter or oxygen sensors. 
3. Monitor the live data from the upstream and downstream oxygen sensors. 
4. A healthy downstream oxygen sensor reading should be a steady voltage (around 0.6 to 0.8 volts) at idle and when revving, while the upstream sensor fluctuates. 
5. If the downstream sensor's reading oscillates or dips, it could indicate a bad converter. 

Vacuum gauge test

1. Locate a vacuum port on the engine and connect a vacuum gauge.
2. At idle, note the baseline vacuum reading (a typical reading is 16-21 inches of mercury).
3. Have a helper rev the engine to about 2500 RPM.
4. With a healthy exhaust, the vacuum should briefly drop and then return to the baseline.
5. If the vacuum drops and takes a long time to return, or stays low, it can indicate a blockage in the exhaust system, likely from a bad catalytic converter. 

Other diagnostic methods

• Listen for rattles: Tap the converter with a rubber mallet and listen for any rattling sounds, which could indicate broken internal parts.
• Power test: Loosen the bolts before the converter and see if there is an increase in engine power, which would point to a clogged converter. 

Which cars are most likely to have a catalytic converter stolen?

Cars most likely to have their catalytic converters stolen include models with high ground clearance, like trucks and SUVs, and hybrid vehicles, with the Toyota Prius and various Honda models topping many lists. Specific models frequently targeted are the Ford F-Series, Honda Accord, and Honda CR-V, because they are easy to access and contain valuable precious metals like platinum, palladium, and rhodium. 
Popular targets by vehicle type

• Trucks and SUVs: These are prime targets because their high ride height provides easy access underneath the vehicle. 
  • Ford F-Series (especially the F-150) 
  • Ford Explorer 
  • Chevrolet Traverse 
  • Chevrolet Silverado 
• Hybrids: These vehicles are often targeted because their catalytic converters tend to be in better condition and have higher concentrations of precious metals. 
  • Toyota Prius 
• Sedans: Certain sedans are also frequently stolen from. 
  • Honda Accord 
  • Toyota Camry 
  • Honda CR-V