Symptoms of a Bad Catalytic Converter

A catalytic converter serves as an exhaust emission control device that reduces toxic gases and pollutants as the engine's exhaust gas passes through it.

The catalytic converter may get clogged, which leads to exhaust gases being restricted, which leads to a check engine coming on, engine misfire, and lack of power. A bad catalytic converter will cause several symptoms that can not be easily missed.

When the catalytic converter gets clogged, it restricts the exhaust flow, which leads to less air getting into the engine. This leads to engine misfire, check engine light flashing,  poor acceleration, engine problems, and check engine light coming on. 

Symptoms of a Bad Catalytic Converter

Bad Catalytic  Converter

The most common symptoms of a bad catalytic converter are:

  • Backfiring
  • Poor acceleration
  • Check engine light on or flashing.
  • Sluggish engine performance
  • Dark exhaust smoke
  • Excessive heating coming from under the vehicle
  • Engine overheating
  • Rotten eggs smell from the exhaust.
  • Exhaust smoke
  • Excessive exhaust temperature
  • Decreased engine performance
  • Failed emission or smog test
  • In some cases, the car won’t’ start.
  • Fault codes preset 

Some of these symptoms may be caused by related issues such as bad spark plugs, ignition coil, air filter, fuel filter, fuel pump, and other issues. The proper diagnostic is recommended before replacing the catalytic converter. 

How to Test for a Bad Catalytic Converter

bad catalytic converter

A catalytic converter does not need to be removed to be tested. A common symptom of a bad catalytic converter is a red glowing catalytic converter. 

An experienced auto mechanic can spot a bad catalytic converter quickly based on the symptoms. It is highly recommended to perform one or more tests to verify that the catalytic converter is indeed faulty before replacement.

Here are a few tests that can be performed to test a catalytic converter: 

  • Temperature test -    Let the car warm up to operating temperature. Lift the vehicle on a lift but leave the engine running.   Use an infrared thermometer to measure the temperature at the inlet of the converter.  Then, measure the temperature at the converter's outlet, where it feeds back to the exhaust pipe.  Because the conversion process produces heat, the outlet pipe's temperature should be higher than the temperature at the inlet.  If the opposite is true, the converter is clogged or broken.
  • Sound test - You can also tell if a converter is broken by simply hitting it with a mallet.  Do this when the engine is off and the converter is cold.  Crawl under the car, find the converter and hit it with your hand.  If you hear debris rattling around inside, the honeycomb in the converter is broken, and you need a new one.
  • Exhaust backpressure test. This is not a test that you can do yourself. An exhaust back pressure test will need to be performed by an auto mechanic or a muffler shop. The mechanic will drill a small hole in the catalytic converter's front and insert a small probe attached to a gauge. The engine is started, and the exhaust back pressure is measured with a gauge. If there is excessive pressure buildup, it will show that you have a clogged catalytic converter restricting the exhaust gases.

What does a bad catalytic converter sound like?

It's not easy to identify a bad catalytic converter by sound because a bad catalytic converter itself will not make any unusual sounds even when it is clogged.

Instead, pay attention to the car not idling properly or the engine running rough.  This is because the exhaust gases are not passing through the converter properly and are not making it out of the tailpipe, which causes backpressure, and the engine does not run properly.  

You may hear broken pieces rattling inside the converter when you hit it with a mallet. 

What does a bad catalytic converter look like? 

catalytic converter

One way to tell if the catalytic converter is bad is to look at it after the vehicle has been run for at least 15 minutes.

overheating cataltyic converter

If the catalytic converter is bad, it will glow red. This signifies that either the catalytic converter is clogged or fuel is burned in the catalytic converter, typically due to a bad spark plug or ignition coil. 

Can you drive a car with a bad catalytic converter?

While the engine may still run, we wouldn’t recommend driving a vehicle with a bad catalytic converter.  If the converter is bad, the car will not run properly, leading to more damage to the engine if not fixed.  

How do you unclog a catalytic converter?

Catalytic converter cleaner

It is possible to clean a blocked converter.  You will need a bottle of catalytic converter cleaner, available at auto parts stores or online. Pour the additive into your fuel tank.  We recommend doing this when your gas tank is full so that there is an even mix of cleaner and fuel.  

However, keep in mind that this will only work on a partially clogged converter, and a completely blocked converter should be replaced as soon as possible.

How long does a catalytic converter last? 

Most catalytic converters last about 8 to 10 years. On the other hand, we have seen a few catalytic converters fail as early as five years, and some last up to 20 years.

If your catalytic converter is only lasting a couple of years, this can be due to an engine problem or a poorly maintained vehicle. When the catalytic converter fails, it will get clogged, lead to poor acceleration, mostly uphill, check engine light coming on, and even engine overheating or shutting down. 

How to maintain a catalytic converter? 

bad spark plugs ruin catalytic converters

Doing basic tune-up such as changing engine oil spark plugs, engine air filter on time will make your catalytic converter last longer. To make a catalytic converter last longer, make sure to keep your engine running at its best.

How much does it cost to replace the catalytic converter? 

Changing the catalytic converter is an expensive repair. The cost to change the catalytic converter can range from as low as $800 to $3000 for a direct fitment (OEM) catalytic converter.

A cheaper alternative is to visit a muffler shop and install a universal catalytic converter. A universal catalytic converter costs from $300 to $500. Instead of replacing the whole catalytic converter and the pipes, a muffler shop will cut out the catalytic converter and weld a universal catalytic converter.

We have had universal catalytic converters installed on many vehicles. They work just as good as the OEM catalytic converters. The check engine light can then be reset, and you can now pass your emission test. 

Why does a catalytic converter fail? 

One of the most common problems that lead to the premature failure of the catalytic converter is worn spark plugs. When the spark plugs are not replaced at the recommended interval, they wear out, which leads to fuel not completely getting burned in the engine. Fuel exits the engine with exhaust gases but ends up getting burned in the catalytic converter, which leads to its premature failure. 

How many catalytic converters does a car have? 

Cars that have a four-cylinder engine have only one catalytic converter. 

Cars that have six, eight, ten, or twelve cylinders typically have two catalytic converts. 

By  YOUCANIC Automotive Experts

Published on: Friday, August 28, 2020.
Updated on: Wednesday, December 30, 2020