Bad Catalytic Converter: Is it worth fixing on a junk car?

You may not know what a catalytic converter is, or what it does, but if your catalytic converter goes bad, you will have to deal with it. Your catalytic converter is a key component of your car's emission control system. So it must be operational to keep your vehicle running right and also to keep it legal!

Join us for an insider's view of what a catalytic converter is, what it does, what makes your catalytic converter go bad, how to know if it goes bad, how to fix or replace your catalytic converter, what a replacement cost, breaking in a new catalytic converter, the risk of having your catalytic converter stolen, and finally, whether it is worth fixing a bad catalytic converter.

What is a catalytic converter, and what does it do?

The catalytic converter is a metal canister that is a part of your car's emission control system. It is usually located between your engine's exhaust manifold and the muffler. Your catalytic converter looks somewhat like a muffler, but it is much different, inside and out. Its case is made of stainless steel, to withstand corrosion and high exhaust temperatures. Inside, it has a ceramic honeycomb structure that is coated with precious metals like platinum, palladium, and rhodium.

As the exhaust gases from your engine flow through the catalytic converter, the remaining unburned gases from the combustion process chemically react with the precious metals inside, at a temperature of around 800°F. This "catalytic" process "converts" these smog-producing chemicals and by-products (carbon monoxide, nitrogen oxides, unburned hydrocarbons) into safe, non-polluting substances like carbon dioxide, nitrogen, oxygen, and water vapor.

Most gasoline-powered engines built since 1975 have one or more catalytic converters, as a result of efforts to reduce air pollution.

What makes a catalytic converter go bad?

While most catalytic converters will last the vehicle's life, exceptions exist. If coolant, oil, or unburned fuel gets into the catalytic converter, gets damaged from the outside, or even wears out, your catalytic converter can go bad. Here are some of the causes of a bad catalytic converter:

  • High mileage
  • Bad fuel injectors
  • Bad spark plugs
  • Bad exhaust valves
  • Weak ignition system
  • Bad head gasket
  • Intake manifold leak
  • Use of leaded gas
  • Failed oxygen sensor
  • Impacts from road debris or curbs

How can you tell that your catalytic converter is bad?

Several symptoms can tell you that you have a bad catalytic converter. Here's the list:

Reduced performance and/or starting problems

The ceramic honeycomb structure inside your catalytic converter can deteriorate, become damaged, and break apart into pieces. This can be a result of age, impacts, or other causes. When this happens, the catalytic converter can become clogged, restricting the normal flow of exhaust gases and the rest of the system. This will directly affect the engine's performance to the point where you may not even be able to get your car started. You may notice:

  • A lack of power
  • Poor acceleration
  • The need to accelerate harder to get an acceptable amount of power
  • Hesitation
  • Misfiring
  • Stalling
  • A drop in fuel economy
  • The engine won't start

A rattling sound from underneath your car

If the ceramic pieces inside your catalytic converter break up into smaller pieces, you may hear them rattling around inside it when the engine is starting, running, or when your car hits a bump or a pothole.

A sulfurous, rotten egg smell from your exhaust

During the combustion process inside your engine, the sulfur in your gasoline becomes smelly hydrogen sulfide gas after the fuel-air mixture is burned in the cylinders. Under normal conditions, the hydrogen sulfide is converted into odorless sulfur dioxide when your catalytic converter works correctly. A bad catalytic converter will be unable to convert the hydrogen sulfide, so it will come out of your exhaust unprocessed, smelling like rotten eggs - a very objectionable odor.

Your Check Engine light comes on

The engine computer in your car constantly monitors the condition of all the emissions-related equipment in your vehicle. If the computer detects that your catalytic converter is not working correctly, it will illuminate the Check Engine light on your dashboard. A trouble code will also be indicated on the computer, which a mechanic can retrieve. This will help the mechanic track down the exact cause of the problem.

You fail an emissions test

If you live in an area where your car must have its emissions tested, you may find out that you have a bad catalytic converter when it fails a mandated vehicle emissions or smog test. This could be because the test discovers a catalytic converter-related trouble code in your engine computer (in which case your Check Engine light is probably lit up), or because the test revealed an excess of unburned gasoline in your exhaust.

How to fix a bad catalytic converter

There are a few different strategies for fixing a bad catalytic converter. We will start with the least expensive first, and work our way up to the most expensive. You should be able to manage the first two, but the last two should be left to a mechanic:

1. The Italian tune-up

If you do a lot of stop-and-go driving at low-to-moderate speeds or never accelerate hard enough to get your car and catalytic converter thoroughly warmed up, the "Italian tune-up" may work for you. By going out on a highway with very little traffic, accelerating hard repeatedly, and running at higher speeds for a prolonged period, you may be able to burn off deposits that have accumulated in your catalytic converter. This can improve the efficiency of your catalytic converter and restore its performance - and it costs you nothing!

2. Catalytic Converter Cleaner

Let's say that you find yourself in a position where you need to pass a smog test, but your Check Engine light is on and indicates that you have a bad catalytic converter. In addition, you don't have any other indications (rattling, bad smells, etc.) that your catalytic converter is terminal. Before you spring for a new catalytic converter, give this a try. You add a bottle of this product to your gas tank when it is ¼ full, then fill the tank, have a mechanic clear the trouble code, and drive until the system recycles (usually around 100 miles). If the Check Engine light stays off, the cleaner has likely worked, and you should immediately have your car tested. There is no guarantee with this method, but at around $25.00 out of pocket, it does not cost much to try it.

3. Universal-Fit Catalytic Converter Replacement

If your car is registered in a locality that permits it (check your local regulations), you may be able to replace your bad catalytic converter with a less expensive universal catalytic converter. This will cost you much less than a catalytic converter made specifically for your vehicle. The only downside is that the installation may cost more, but you should still proceed.

4. OEM Catalytic Converter Replacement

Also known as direct-fit, this is a replacement catalytic converter that is designed to fit and work on your specific vehicle. It will cost significantly more than the universal-fit catalytic converter but will be easily and quickly installed.

A word about states with strict emissions regulations

In states like California and some others, replacement catalytic converters must be registered with and approved by the state's Air Resources Board. These catalytic converters are stamped with an EO (Executive Order) number specific to your vehicle, are the only type of catalytic converter replacements that are allowed, and are very expensive! The good news is that you are exempt from this requirement if your car is over five years old, and its manufacturer's emissions warranty has expired. Again, check your local regulations to determine what is allowed under the law.

What does it cost to replace your catalytic converter?

As with most car repairs, prices vary widely, depending on who is doing the job, the degree of difficulty, and the cost of the parts. Because the catalytic converter lives underneath your car in a hostile environment, there can be rusted bolts and pipes for the mechanic to deal with, as well as oxygen sensors, exhaust pipes, and mufflers that could also need repair or replacement.

Depending on your car's year, make, and model, replacing the catalytic converter could run anywhere from a few hundred dollars to a few thousand dollars. The best action is to visit several well-rated repair shops and get firm estimates for your specific vehicle's catalytic converter replacement costs. Try muffler specialists as well as general-purpose repair shops.

Check your emission warranty - you might be covered!

If your car is less than eight years old and has less than 80,000 miles, your catalytic converter should still be covered by the manufacturer's Federal emissions warranty. This means a replacement catalytic converter could be provided at no cost! Contact the service department of your vehicle brand's local new-car dealer to verify your eligibility under the warranty terms.

Do you have to break in a new catalytic converter?

A break-in procedure for a newly installed catalytic converter should be followed to ensure a long, trouble-free life. Ideally, this should be done by your mechanic as part of the installation procedure, and you should verify in advance that this will be taken care of. If the mechanic does not break in your new catalytic converter, here is how to do it, quickly and easily:

  • Start the engine, let it idle, and slowly warm up for five minutes
  • Increase your engine speed to 2,500 rpm and hold it there for two minutes
  • Let the engine cool down

That's it - do this and you're good to go!

Should you worry about thieves stealing your catalytic converter?

Because catalytic converters have precious metals like platinum inside, they are expensive. Thieves will target catalytic converters because they hang exposed underneath your car and are easily accessible. A thief can roll himself under a vehicle with a cordless cutting tool, cut through the pipes on each end of the catalytic converter, and be gone with it within minutes. Vehicles with high ground clearance, like SUVs and pickup trucks, are the easiest and most likely targets. Lower vehicles like cars usually need to be jacked up first. The thieves will then sell the stolen catalytic converters to unethical scrap yards or auto recyclers.

How can you tell if your catalytic converter has been stolen?

This is an easy one - your exhaust will sound very loud because a piece of the system is missing. You will know immediately, the first time you start your car!

How can you prevent your catalytic converter from being stolen?

Your parking spot needs to be as secure as possible. A locked garage is best, followed by a well-lit gated parking area with video surveillance. Park near the lot's entrance, which has the most foot traffic. If you have a security system on your vehicle that senses vibrations from a cutting saw, that can help.

You could engrave your car's VIN on the catalytic converter to aid in identification and possibly deter thieves. You can install theft-deterrent devices - they make it much more difficult to steal your catalytic converter quickly, so hopefully the thieves will move on to an easier target.

Is it worth replacing your catalytic converter?

Due to the cost involved, replacing your catalytic converter should be considered a last resort. This is especially true if your car is very old, has many miles on it, is not exceptionally reliable, and you live in a state with strict smog laws.

Unless your catalytic converter is physically kaput, there are several things that you should try first, before spending the money on a new one. Start by having a mechanic eliminate other possible causes of your symptoms by checking for things like:

  • Exhaust leaks
  • Bad oxygen sensor
  • Wiring problems
  • Computer trouble codes that are not catalytic converter-related
  • Proper engine operation - is routine service required?

Once you have eliminated all non-catalytic converter issues, try the Italian tune-up first, then the catalytic converter cleaner. If these don't work, and you are facing the need to lay out the cash for a replacement catalytic converter, you have a decision to make. Here are some questions to ask yourself:

  • What will it cost to replace the catalytic converter, including installation?
  • What is your car worth?
  • How many miles are on it?
  • Does your car have any other chronic issues that could result in a significant repair soon?
  • Will the brakes or tires need replacement soon? Is it time to cut your losses and get rid of your car now?

Is it worth selling your bad catalytic converter?

If you have a junk car with a bad catalytic converter, you may wonder if it's worth selling the catalytic converter before selling it as scrap. While it is true that catalytic converters contain valuable metals such as platinum, palladium, and rhodium, the decision to sell the catalytic converter depends on a few factors.

If the car is still in decent condition and the catalytic converter is the only major issue, replacing the catalytic converter may be worth it. If the car is in poor condition and the cost of replacing the converter outweighs the potential profit from selling the car, it may be a better choice to sell the catalytic converter separately. will buy your car for cash today!

If you have run the numbers and concluded that it is not worth investing in a new catalytic converter for your car, we can help! Get an instant quote to sell your car for cash today from Junk Car Medics®, the nation's premier online car-selling service trusted monthly by thousands.

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