FAQs & Tech Info

Do catalytic converter shields work?

With more and more catalytic converter theft, converter theft prevention and shield awareness is growing and people want to know how effective these anti-theft devices are before investing for their own vehicle. This is understandable since, depending on the make and model of the vehicle, catalytic converter shield cost can come as a surprise. However, when considering the cost of replacing a catalytic converter and the effectiveness of catalytic converter shields, the investment is worthwhile. In short, catalytic converter shields work and protect your vehicle. High-quality converter protection devices like Cat Shield™ by MillerCat make it difficult for thieves to cut through. The added time and effort it takes to tamper with the 304 stainless steel shield can deter would-be thieves from targeting your vehicle in the first place. 

304 stainless steel

What cars are most targeted for catalytic converter theft?

Although any vehicle can be at risk for catalytic converter theft, specific models appear more targeted than others. According to CarFax, location matters and the most targeted vehicles can vary from coast to coast. Those who live in the western states see a spike in catalytic converter theft among the Toyota Prius, Subaru models, and Ford F-Series and Econoline. To the eastern portion of the US, we also see Subaru models, Toyota, and Ford models. In the south, we see an uptick in theft in sedans, such as the Chevrolet Cruze and Dodge Avenger. And making the top 10 in the midwest, we see a high rate of catalytic converter theft in Chrysler 200 and Jeep Patriot. Nationwide, there is no pattern of a single body style or manufacturer, however, hybrid cars, luxury cars, and trucks top the lists because of the value of the precious metals, such as rhodium, palladium, and platinum.

Which cars are least likely to have catalytic converters stolen?

Specific vehicle models are not as attractive to thieves. Vehicles whose catalytic converter contains less valuable or fewer precious metals often get overlooked, such as non-hybrid Ford, Mazda, and Chevrolet models. Age can play a role, too. Automobiles manufactured before 1974 are least likely to have catalytic converters stolen because they were not installed during this time. Electric cars are not at risk since these cars rely on electricity for power rather than fuel, eliminating the need for reduced emissions and catalytic converter installation.  

How much does a catalytic converter replacement cost?

If a victim of converter theft, the first thought is often how much to replace a catalytic converter. Catalytic converter replacement cost can widely vary. Just as thieves target converters of higher value, several factors can affect the replacement cost, including the quality of the replacement part, the make and model of the vehicle, cost of labor, and any other additional diagnostic or parts and repairs fees. Most full or comprehensive car insurance plans cover replacement, however, those with liability-only coverage will pay out of pocket. Depending on your location and vehicle model, catalytic replacement costs can run from $1,000 to $3,000. 

How to know if a catalytic converter is stolen?

When a catalytic converter is stolen, the automobile will give tell-tale signs. At ignition, the vehicle will make a roaring sound and get louder when accelerating. The vehicle may “sputter” while in drive with increased exhaust fumes and odd smells, such as rotten eggs. The “Check Engine” light may appear and drivers will probably experience a shift in the car’s performance and fuel economy. And, of course, without the catalytic converter, a failed emissions test is inevitable. 

What does a catalytic converter shield do?

A catalytic converter shield is a protective barrier between the converter and thieves and can help prevent catalytic converter theft. The best catalytic converter shields offer the ultimate security with the highest quality materials, such as stainless steel and advanced engineering and design technologies supplying optimum protection. 

Can thieves cut through Cat Shield™ by MillerCat?

Even when taking precautions and installing anti-theft catalytic converter shields, the unfortunate can happen. Given enough time and the right tools, thieves can cut through a low quality catalytic converter shield. When attempting to cut through MillerCAT’s Cat Shield™, the amount of noise and time can make thieves reconsider. This is because of the intricate design and superior materials of a MillerCat Cat Shield™. Not even a Milwaukee Super Sawzall and Diablo carbide tip blade can stand up against our 304 stainless steel shield.  

Why are people stealing Prius converters?

Many people ask why their Prius converters are being stolen in record numbers. Why do people target a hybrid vs a large truck? Aren’t Prius’s suppose to be clean vehicles? The answer is Palladium and Rhodium. It is true that Prius’s are clean and are classified at the Super Ultra-Low Emissions Vehicle (SULEV) level, but in order to obtain that classification Toyota had to ensure the Prius passed a strict emissions test. The reason hybrids have some of the highest precious metal content out of any vehicle is because hybrids turn on and off their gasoline engines frequently to save gas. However, most of the harmful emissions are produced during the initial start of the engine called a cold start. A catalytic converter needs to reach an optimal temperature to efficiently convert harmful gases, but frequent cold starts constantly lowers that temperature and makes the converter inefficient at reducing harmful emissions.

In order to solve this problem Toyota overloaded their hybrid converters with palladium and rhodium. 10-15 years ago (2004-2010), palladium was only around $200-$300 per troy ounce and rhodium averaged around $3,000. Today, palladium is around $2,600 and rhodium is around $27,000. At the time Toyota designed their converters, the price of metals was cheap, but due to global supply constraints and rising need for cleaner cars, the prices of those metals jumped upwards of 700% for palladium and 300% for rhodium in the past few years.

Due to these factors thieves are making the most money off of Prius converters and making life harder for Prius owners. We highly recommend our Cat Shield to prevent such theft and to protect your investment. Let us know if you have any questions that aren’t answered here.

Does the Cat Shield make my car hotter?

We’ve done extensive testing on the front and rear converters with and without the Cat Shield under numerous driving conditions. Our data reveals that during city or freeway driving, there is minimum temperature increases (10 degrees max) and there is actually lower temperatures with the Cat Shield at the rear position when driving on the freeway. This is likely due to the Cat Shield making the vehicle more aerodynamic, which reduces turbulence, and makes the louvers more effective at drawing out heat.

Even right after spirited driving and when the car is turned off, the Cat Shield will be safe to touch (although we recommend using proper safety equipment like gloves at all times). Temperatures at different points of the shield on average were 80 degrees. We also measured temperatures on the underbody of the car near the hottest points (front and rear converters) and saw consistent and similar temperatures of 80-200 degrees.

Based on the temperature data, we conclude that the shield will have no impact on increased cabin temperature, will not pose increased danger to flammable material underneath the car (in fact, the shield protects material from touching the hottest part of the exhaust, the converter/s.), or prematurely wear down exhaust components.

What about galvanic rust or corrosion?


Some competing products will use rivets or say their hardware is corrosion-resistant, but when differing corrosion-resistant metals come into contact, they will corrode by a process called galvanic corrosion (also called bimetallic corrosion). Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. Basically, it is when two different metals come into contact with each other, they can cause premature rust and corrosion.

We use all stainless steel hardware and zinc coated rivet nuts to prevent rust and corrosion. The underneath steel frames of the Prius are coated and do not come into direct contact with the aluminum shield. Even after drilling holes into the frame, the zinc-coated rivet nuts are the only pieces that touch any uncoated steel and the zinc acts a protective barrier between the metals. We take every piece of hardware into consideration to make sure none of our parts will cause premature rust or corrosion. Be wary of products that do not use stainless steel or zinc-coated materials (such as rivets, self-tapping nuts or screws) because they will likely lead to galvanic rust.

What are the benefits of louver vents?

All our Cat Shields are designed with louver vents to give our customers the best product on the market. They are not simply there for looks, but help cool your vehicle and protect it from debris. The graphics below show the scientific reason behind our design.

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Why rivet nuts?

Rivet nuts are great pieces of hardware that allows one to get threaded holes where there once wasn’t any. Understanding the need to replace O2 sensors and doing other maintenance to the vehicle, we designed our Shield for rivet nuts. This way you can take on and off the shield yourself and not do any damage to the shield or vehicle. Our tamper-proof screws coupled with the rivet nuts provides the best combination of protection and convenience.

Will the Cat Shield void my warranty?

There are many dealers who are selling the Cat Shield and installing them on customer vehicles. While we cannot guarantee an issue could arise, nothing on the exhaust system should be voided because of the shield. If there is ever any doubt, our Shields are removable which should ease any concern you might have.

Why do you use spacers and noise dampeners?

We thoroughly test and develop our products with you in mind. You cannot just place a sheet of metal underneath the car and not expect to have noise and vibrations. We’ve considered almost every variable such as the movement of the converter, exhaust system, engine, and angles and planes of mounting points, in our design. We use spacers and noise dampeners to ensure that the only time you know the shield is on is if you look below the vehicle. The Prius Liftback, Prius C, and Prius V specifically use spacers and dampeners.

What type of aluminum is the Cat Shield made from?

We use 5052 grade aluminum, which was purposely chosen because of its strength and for its excellent saltwater resistance. For those customers near bodies of ocean or in areas where roads are heavily salted, our shields are for you!

Can’t someone just cut the shield?

There is no perfect deterrence against catalytic converter theft. Anybody with the right tools, time and willingness can remove any anti-theft protection device. Our goal has been to deter the thief as much as possible. We have proven deterrence from our customers that show thieves see the shield and move on. If someone tried to cut off the shield, they will create a lot of noise and take a lot of time to get off the shield. When a thief is looking only to spend a few minutes to steal a converter, they will think twice when the job will require different tools, more time, and more noise. We’ve tested our shield against a sawzall, it is not pretty and definitely loud and time-consuming.

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