5 Symptoms of a Bad Catalytic Converter (and Replacement Cost)

The catalytic converter (not “Cadillac converter”) plays an essential role in reducing air pollution. It reduces the levels of nitrogen oxide, hydrocarbons, and carbon monoxide that your car emits. Without a cat converter, your vehicle would belch out large amounts of all three chemicals. 

Smog in busy cities is dense enough as it is without adding to this complication. Not only that, but the three gases can have severe effects on the environment if emitted indefinitely.

Carbon monoxide can poison us. Nitrogen oxide and hydrocarbons, once unleashed, are combined with humidity to form acid rain. Our cat converters are a crucial part of keeping our home pollutant-free and keeping us safe on the road.

See Also: 5 Cars LEAST Likely to Have Their Catalytic Converter Stolen

How a Catalytic Converter Works

how catalytic converter works

The mechanism is simple. It’s a big metal box that manufacturers place underneath your car. It has two tubes coming out of it: the input and the output.

The input connects to your engine. The fumes created by the engine feed into the input, and the vapors then pass over a catalyst in the main container. When this happens, a chemical reaction takes place to bind the harmful compounds and clean the air.

The output is used once the fumes have passed over the catalyst. The fumes are no longer dangerous, so they are fed through the output to the exhaust.

Over time, the catalyst becomes less efficient or even breaks apart, and you’ll need to replace the system completely.

Bad or Clogged Catalytic Converter Symptoms

The catalytic converter is a critical component in the exhaust system of your vehicle. You need to watch for signs of a clogged catalytic converter going bad. Here are five of the most common signs of a bad catalytic converter:

1) Sluggish Engine Performance

car hesitates when accelerating - gas pedal

Unless the converter is blocked, this is not a fatal error. Your car is not going to stall, but it is also not going to operate at peak efficiency. If you keep ignoring the problem, your car will eventually fail.

When the converter is not working optimally, the gases aren’t led out of the engine efficiently. It makes it harder for the engine to operate at peak efficiency. You’ll still be able to accelerate, but responses will be sluggish.

The first step should be to use a good catalytic converter cleaner to see if that helps clean and unclog the partial blockage. You should always start with the quickest and cheapest fix. 

2) Rattling Sound From Under Vehicle

rattling sound

If you start to hear a rattling noise coming from underneath your car, there’s a possibility some of the honeycomb material inside the catalytic converter has broken apart. This would cause it to hit the insides of the cat converter as the car is driving or simply from the exhaust flow.

The noise is often loudest when first starting your car and can get worse as additional pieces break off. Get the catalytic converter replaced asap before one of those chunks makes its way down to the muffler where it can cause a complete blockage.

See Also: Signs You May Have a Hole in Your Muffler

3) Dark Smoke From Exhaust

car exhaust smoke

A sure sign that something is wrong, it will also alert road authorities to the condition of your car. If there’s black smoke belching out of the exhaust, it’s safer not to drive the vehicle until your mechanic has fixed it.

4) Distinctive Sulfur Odor

car smells like rotten eggs

You know that smell when an egg has turned rotten? That’s the smell we’re talking about here.

With a properly functioning converter, smelly sulfide is converted into sulfur dioxide which is odorless. If the catalytic converter is not working correctly, this chemical conversion doesn’t take place.

5) Heat Buildup Underneath Car

driver too warm inside car

The gases coming out of the engine are extremely hot. If you don’t remove these, they’ll build up under the car, and the entire area will get too hot. You may feel the extra heat right outside one of the doors or even inside the cabin after a long drive.

The only way to know for sure if there’s something wrong with your cat is to take your vehicle to the mechanic. A standard cat system should last at least eight years or about 80,000 miles. If you look after your vehicle well, you can easily stretch that to over ten years or more.

Taking proper care of your vehicle is simple:

  • Don’t skip any minor or major services.
  • Regularly scan for codes whenever you see a check engine light so that you pick up problems fast.
  • A blocked fuel or air filter can cause some big problems for you here, so keep that clear.

Catalytic Converter Replacement Cost

We recommend Parts Geek for the best prices and selection.

catalytic converter replacement cost

Costs here are difficult to pin down. It all depends on the make and model of your cat converter.

A two-way cat converter is between $100 and $600, depending on what make and model of vehicle you own. In terms of labor, this is a reasonably simple job. If all goes well, it shouldn’t take more than about an hour. So, tack on around $75 to $120 for labor.

You’ll usually find two-way models in older cars. Thanks to the more straightforward design, they’re easier to fit. Unfortunately, it may be difficult to find parts for older vehicles.

A three-way converter is more expensive and commonly found in cars running on gas and made after 1981. Much depends on the make and model of the vehicle, and you’re looking at between $600 and $2,500 for a replacement.

Installation doesn’t take long, so work on about an hour’s worth of labor.

Keep in mind that the Federal Emissions Warranty comes into play here, too. Your converter must last for 80,000 miles or eight years, whichever comes first. If you haven’t reached 80,000 miles or eight years, you should still be under warranty.

Thieves often target cat converters due to the precious metals (platinum, palladium, and rhodium) contained within as scrapping them can earn them $100 to $200 per cat. You can help prevent this theft by welding metal to the converter, putting on a lock, and etching your name into the metal.

See Also: 5 Ways to Tell Your Catalytic Converter Was Stolen

Can You Drive with a Bad Catalytic Converter?   

Driving it to the mechanic won’t do the car any harm. You could drive indefinitely with this issue, as long as the converter is not clogged. It would be unpleasant for those behind you, though.

You’ll notice the same horrid odor from the car until you clean out the catalytic converter. Nine times out of ten, the only thing that will take you off the road here is the police. If they stop your car, you’ll face a hefty fine because of the emissions.

You will notice that the car becomes less efficient over time, too. The longer you put off fixing the problem, the better your chances of a wholly blocked catalyst, which is something that will stop your vehicle in its tracks.


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