See How Do You Check For A Bad Catalytic Converter In 4 Easy Methods

How do you check for a bad catalytic converter? You’ll be surprised to hear that a vacuum gauge can get the job done. Also, a back pressure gauge or rubber mallet, or hammer is a great tool to check a catalytic converter.

Even if you don’t have these tools, there is another way to follow. The following details are everything about the catalytic converter checking and its maintenance. Keep on reading and know the answer elaborately.

How Do You Check For A Bad Catalytic Converter: 4 Ways To Follow

To determine whether your catalytic converter is bad, there are several tests you can go for. You may require some useful tools to do these tests. These appliances are available in any repair shop. So, don’t be worried and move on.

Test – 1: Vacuum Test

If you suspect your catalytic converter is clogged you can check it through a vacuum gauge. But, how do you check for a clogged catalytic converter with a vacuum gauge? Let’s follow the steps below.

  • First, apply the parking brake of the gauge and set the transmission to either automatic or manual mode.
  • Disconnect the hose from the power booster and connect the vacuum gauge to it. You can also use an intake manifold port to connect it with the hose.
  • Now, start the engine and let it run for about 20 mins. The engine must come to the temperature for the operation.
  • At idle, the vacuum reading must be 18 to 22 inches top.
  • Increase the speed up to 3000 rpm and notice if the vacuum reading is dropping and going back again to the previous level. If it isn’t happening, the catalytic converter is most likely clogged. To be more sure, go for the next step.
  • Now repeat the test with an engine speed of 2000 rpm. Notice every snap of the throttle in vacuum reading. If the gauge needle continuously drops nearly zero, then there’s a strong possibility that your converter is clogged.

Test – 2: The Back Pressure Test

The back pressure test is done directly in the exhaust system. To do this test, you need a back pressure gauge. Find this tool at your nearest auto-parts store and move on.

  • Start the engine and let it idle for 20 mins. You better stride ahead on a highway, and drive for 20 mins, then return to your garage.
  • Jack up your car safely. Remove the front oxygen sensor. And through the help of some wooden blocks, block the rear wheels.
  • Install back pressure gauge in place of the oxygen sensor.
  • Start the engine and take note of the gauge reading.
  • When you are at the speed of 2500 rpm, the pressure reading should be between 1 and 3 psi. Reading higher than this indicates your catalytic converter is clogged.

Test – 3: The Temperature Test

The temperature test is also an easier test to do. For this, you need an infrared thermometer. When the trouble code shows up, you can check this temperature test.

  • Park your car on a flat surface and put the transmission in either auto or manual mode.
  • raise your vehicle to get easy access to your catalytic converter.
  • Start the engine and idle it for 20 mins so that it comes to the operating temperature.
  • Notice the temperature of the inlet pipe while the engine is on. Note the temperature reading.
  • Now take note of the outlet pipes’ temperature reading that connects to the rear catalytic converter.

If the converter is bad, the temperature of the inlet pipe will be the same or higher than the outlet pipe’s temperature.

Test – 4: The Tapping Test

The tap test ensures the physical condition of a catalytic converter. This is a tool for free catalytic converter check. You will need a rubber mallet or a regular hammer to do this test.

  • Raise the front part of your vehicle if you need easy access to your converter. Every time use the jerk stands to do it.
  • Apply the parking brake choking the rear wheels.
  • Use the mallet or the hammer and tap on the converter.
  • If you experience a rattling sound, that means the internal parts of your converter have collapsed and you need to replace the converter.

How Do You Know If You Got A Bad Catalytic Converter

A catalytic converter is like the liver of a vehicle. If it gets sick, it’ll show some symptoms. Apart from some technical problems that most truck owners overlook, some common symptoms let you know that you got a bad catalytic converter.

The check engine light will be on if the catalytic converter is clogged. For this, you don’t have to be a mechanical expert. Just peer at your dashboard and get acknowledged.

The other sign is poor acceleration. When you accelerate your vehicle, it won’t perform at its peak. Also, you’ll have trouble starting your vehicle. The vehicle won’t start on the first attempt if your catalytic converter is clogged.

Do you know will an O2 sensor work without a catalytic converter or not?

5 Signs of A Bad Catalytic Converter

Apart from the primary sign of check engine light, starting problem, and poor acceleration, there are several symptoms that a bad catalytic converter has. Let’s take a look to know.

Fuel Efficiency

A vehicle with a bad catalytic gets less oxygen in the engine. Thus the engine has to work harder and consume more fuel than it used to. So, if you have a bad converter, you’ll run out of fuel in a few miles of driving.

Failed Emission Test

The catalytic converter is a useful part of the emission system. Therefore, a bad catalytic converter will fail an emission test. Since the catalytic converter is responsible for vehicle emissions, it’ll let you know whether the converter is working properly.

Reduced Engine Performance

It’s the most important sign of a bad catalytic converter. When the exhaust is trapped in front of the catalytic converter, it reduces the engine performance. And when you push the engine, it’ll feel like no fuel is reaching the engine.

Black Smoke

Less oxygen in the engine creates toxic gasses and transforms the exhaust smoke into a dark color. Whenever the smoke gets black, find a mechanic and figure out underlying issues.

Bad Odor

There’s sulfate in the fuel. When a catalytic converter gets clogged, it smells like rotten eggs. Fixing the converter will reduce the smell entirely.

Frequently Asked Questions (FAQs)

What are three signs of a bad catalytic converter?

The three most common signs of a bad catalytic converter are:
i. Slow engine performance
ii. Sluggish acceleration
iii. Dense black exhaust smoke

Will a bad catalytic converter throw a code?

A bad catalytic converter will give a code. Generally, the check engine will light up first. And then, on the car’s engine module, the diagnostic trouble code P0420 will come up.

Can I unclog my catalytic converter?

It is possible to unclog catalytic converters very easily. Just insert the chemical cleaner into the exhaust system. Circulating the cleaner through the converter will clean everything up.

How do you know if you have a faulty catalytic converter?

Sluggish engine performance is the main sign that indicates the catalytic converter is faulty. Also, you’ll experience some bad odor from the exhaust and reduced acceleration. You may also feel some excessive heat under the vehicle.

How to test to see if your catalytic converter is bad?

To see whether your catalytic converter is bad, you can test it via a vacuum cleaner. Also, a back pressure gauge or rubber mallet helps to check the converter. Even if you don’t have any of these tools, you can go for the temperature test. All the process has been described right above.


When the catalytic converter goes bad, it doesn’t send any proper signal. Instead, some noticeable symptoms appear at that time. The only question that arrives under this circumstance is, how do you check for a bad catalytic converter.

Proper maintenance of the engine, changing the fuel regularly, and checking for leaks of underlying parts are important to keep the converter in good health. You better follow these pro tips for the maintenance of a catalytic converter. The more careful you’ll be for your converter, the more service it’ll offer in return.

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