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Catalytic Converters: What They Do and Why They’re So Darn Appealing to Thieves

If you've been driving long enough, at some point, you've probably experienced catalytic converter problems. Even though catalytic converters are designed to last the life of a vehicle, they often fall victim to overheating and contamination, resulting in an early demise.

What does a catalytic converter do?

The catalytic converter, which is often referred to simply as a "cat", is an emissions control device located in your car's exhaust. Toxic gases from the engine flow through the cat, where they are transformed into harmless CO2 and water.

Inside the converter, precious metals create a type of chemical reaction called a "catalyst" reaction. The reaction cleans up your car's tailpipe emissions making the world a better, more breathable place.

Precious metals in the catalytic converter are highly valuable.

An oxygen sensor sits downstream of the catalytic converter to measure efficiency. Your car's computer monitors the signal from that sensor to ensure the cat is working right.

All vehicles have a least one catalytic converter, though some may have as many as four.

Common catalytic converter problems and symptoms of failure

So, you think you may have a bad catalytic converter? If you have one or more of the following symptoms, you may be correct.

    • Check engine light: The most common sign of a faulty catalytic converter is an illuminated check engine light. Your car's computer will trigger the warning if it detects (via the oxygen sensor) that the cat isn't up to snuff.
    • Reduced power: A clogged or restricted catalytic converter can create excessive exhaust back pressure, which chokes the engine, resulting in a reduction in power.
    • Stalling: Likewise, a cat that's clogged or restricted can create enough exhaust back pressure to case engine stalling.
    • Vehicle won't start: In extreme cases, a bad cat can create enough exhaust back pressure to prevent the vehicle from starting.
    • Failed emissions inspection: A bad catalytic converter will cause your car to fail an emissions test.
    • Rotten egg smell: A good catalytic converter converts stinky sulfur into odorless sulfur dioxide [4]. But if the cat is bad, the sulfur will hang around, creating a rotten egg smell.

What causes it to go bad?

In many instances, catalytic converter failure is the result of an engine-related problem. For example, an overly rich air/fuel mixture can cause the cat to overheat. Contamination from fluids, such as oil and coolant, can ruin a good converter as well.

How to fix a bad catalytic converter

It's pretty straightforward: A bad catalytic converter should be replaced. Before installing the new cat, however, your mechanic should check for engine problems that may have contributed to the failure.

Also, after repair is complete, the check engine light should be turned off using a scan tool or code reader. Because your car's computer doesn't monitor the cat continuously, the light can take a while to extinguish on its own.

When should you replace the catalytic converter?

The catalytic converter should last the lifetime of your car. You'll only need to replace it if it starts acting up.

Average costs of repair and replacement

Catalytic converters aren't cheap. Replacement can cost anywhere from around 500 dollars to a couple of thousand dollars, depending on what type of car you have. If your car is old and unreliable as it is without the cat issue, you might be better off selling than repairing.

Do you have to break in a new catalytic converter?

One thing many people - including some mechanics - don't know is a new catalytic converter should be broken in. Otherwise, the materials inside might not expand correctly, causing the cat to fail later.

Before the car is driven, a new converter should be put through a warm-up cycle to avoid problems. Typically, the procedure starts with idling the engine for five minutes to allow it to warm up. Then, engine speed is increased to 2,500 rpm and held at that speed for two minutes. The engine is then allowed to cool down before being test-driven.

Why do thieves steal catalytic converters?

Remember how we mentioned the catalytic converter contains precious metals? Inside the catalyst portion of the converter, you'll find elements such as palladium, rhodium and platinum. And thieves will cut the cat right out of your car to get at those materials.

Catalytic converters can be sold to metal recycling facilities for a pretty penny. The heist is pretty easy to perform, too. Criminals can unbolt or hack a cat out in less than a minute using simple hand tools. Taller vehicles, like trucks and SUVs, make the job even easier because thieves can get underneath without hassle [1].

How can you tell if it's missing?

You'll know right away if your catalytic converter is missing. Cats are positioned upstream from your car's muffler, so removal unleashes unrestricted engine noise. Your car will make a roaring sound that's loud enough to make you think the engine is ready to explode.

If your car is experiencing such symptoms, take a peek underneath and see if a large section of your exhaust is gone, indicating a missing cat.

How to prevent catalytic converter theft

Does the thought of catalytic converter theft keep you up at night? Then you may want to consider taking a few preventative measures, such as:

    • Parking in well-lit areas or the garage when possible.
    • Engraving your car's VIM number into the catalytic converter (just don't do it while the cat is hot!).
    • Installing surveillance cameras in your home parking area.
    • Adjusting your alarm system so it's sensitive enough to detect vibrations from a thief sawing away at the undercarriage [3].
    • If you're really paranoid, consider a catalytic converter prevention device, such as CatStrap [2].



  1. https://www.allstate.com/tr/car-insurance/catalytic-converter-theft.aspx
  2. https://www.catstrap.net
  3. https://www.yourmechanic.com/article/how-to-prevent-catalytic-converter-theft
  4. https://www.carsdirect.com/car-maintenance/car-exhaust-smell-understanding-where-the-problem-lies
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