Can A Bad Catalytic Converter Cause A Car To Shut Off?

Your car is stalling and wont start. You start to think to yourself, “can a bad catalytic converter cause a car to shut off?”

I’m ASE certified and have taken over 20 course hours of engine drivability diagnostic courses. In those courses, a good portion of time was dedicated to learning how catalytic converters work and how to diagnose them.

As well, I diagnose faulty converters in the field with the latest and up-to-date tools available in the industry today. I can say with positivity that a bad catalytic converter will cause a vehicle to shut off.

 

What Is A Catalytic Converter?

A catalytic converter is a device that is mounted onto your vehicle’s exhaust system. The converter is a chemical catalyst, meaning it changes the molecular structure of chemicals from one to another. 

In your vehicle’s case, the catalytic converter takes harmful, pollutant gasses that are emitted through your exhaust and changes them into less pollutant ones before they are released into the atmosphere. 

The catalyst, usually made out of platinum or palladium, is mounted mid-way through your exhaust. Before the exhaust gasses pass over the catalyst, they are carbon monoxide, hydrocarbons, and nitrogen oxides. 

Once these gasses pass over the precious metal and mix with the heat from the engine, they turn into carbon dioxide, water, and nitrogen. 

The latter chemicals have a much safer impact on the earth’s atmosphere than the former, hence the purpose of the catalytic converter. 

How A Faulty Catalytic Converter Affects Your Engigne

A faulty catalytic converter can cause a number of different issues with your vehicle’s engine performance. The converter is in the exhaust system and any restrictions on your exhaust will hinder your vehicle’s performance. 

There are a couple of different reasons your vehicle’s performance will begin to suffer with an obstruction in your vehicle’s exhaust system. 

The first reason is built up back pressure. Built up back pressure in your exhaust can cause major issues and damage to your vehicle. 

If your exhaust has nowhere to escape to, the exhaust gas will build up in your vehicle’s exhaust system. This will cause pressure in the exhaust system and can even blow out weak spots in the exhaust.

This back pressure can cause your car to have poor performance or even cause your car to stall, shut off, or not start. The back pressure in the exhaust can also find its way up to the vehicle’s oxygen sensor. 

When an oxygen sensor reads that there’s no oxygen in the exhaust gas, the sensor will report to the computer to adjust fuel trim. The adjusting of fuel trim can cause your vehicle to have low performance. 

Another reason why a clogged catalytic converter will shut your car off is because a bad converter is starving your engine of oxygen. An engine can be thought of as an air pump. 

The engine takes air into the cylinder, mixes it with gas, burns the gas, and expels the remnants of the burnt air/fuel mixture. 

If the exhaust gasses cannot be expelled through the exhaust valves, the exhaust gasses will sit in the cylinder, and the cylinder will be full of exhaust instead of air and fuel. 

This will cause lack of combustion since exhaust gasses do not have combustible byproducts in them. In order to have combustion, the combustion chamber must be free of exhaust gasses, and without a safe way to expel exhaust gasses, your engine will not have combustion. 

This lack of combustion will cause your vehicle to shut off, sometimes while driving if the problem gets serious enough. 

Usually, you will be able to notice engine performance issues from a clogged catalytic converter before it gets to the point of shutting your car off while driving though, so don’t ignore any common signs and symptoms of a bad catalytic converter. 

What Are Some Common Signs Of A Faulty Catalytic Converter?

It’s better to catch a faulty catalytic converter before it becomes fully clogged since a fully clogged catalytic converter can ruin your vehicle’s engine. 

Watch out for some of these signs for a faulty converter.

1. Reduced engine performance: A catalytic converter on the verge of failure will cause bad engine performance. You will have reduced accelerating power and have a hard time passing cars on the highway. You will feel like you are receiving no power to your vehicle when you press all the way down on your vehicle’s gas pedal. 

2. Decreased fuel efficiency: A failing catalytic converter could cause decreased fuel efficiency since it makes your engine do extra work to overcome the extra back pressure built up in the exhaust system. If you see a 5-10% decrease in fuel economy, check out your catalytic converter. 

3. A check engine light: Your vehicle has a lambda sensor, which is basically a sensor that checks the effectiveness of your catalytic converter. If your converter is starting to operate below a certain threshold, the sensor will cause your vehicle’s computer to turn a check engine light on. 

4. Excessive Exhaust Smoke: A clogged catalytic converter can cause excessive gray or black exhaust smoke to emit from your tailpipe. The smoke would come out in clouds and be thick and you wouldn’t be able to see through it.  

While there are more intricate signs that could be found through the use of specialized tools, these ones are the most common signs of a catalytic converter that’s failing. If you see any of these signs from your own vehicle, take your car to a shop as soon as possible. 

How To Test A Bad Catalytic Converter

There are many ways to test a bad catalytic converter, but some require special tools. In this section, we’ll go over two ways to test a catalytic converter using tools you can purchase for relatively cheap and at your local parts store. 

The Vacuum Test

Purchase a vacuum gauge and hook it up to a vacuum line in your vehicle. Start your car and note the reading. The vacuum should be around 15-18 in. Hg. 

Now, rev your engine up to 2500 rpm and hold it there. The needle on the gauge will drop down to around 0, and then back up to 18 in. Hg within a few seconds. 

If the needle takes longer than a few seconds to get back up to 18 in. Hg you can suspect a faulty or clogged catalytic converter. 

The Temperature Test

Bring your vehicle up to operating temperature by starting it and allowing the vehicle to run in idle for about 10 – 15 minutes. 

Take an infrared thermometer and point it at the top of the catalytic converter and note the operating temperature. Next, take the thermometer and point it at the bottom of the catalytic converter and note the temperature. 

If the temperature between the top and bottom of the catalytic converter has a difference of anywhere between 50-100 degrees, you can suspect the catalytic converter is clogged or it has lost its efficiency. 

These two simple ways to check your catalytic converter at home will leave you with a better understanding of the state of your catalytic converter. If you suspect your catalytic converter is giving your vehicle engine troubles, try them out and know for sure. 

Key Takeaways

• A bad catalytic converter can cause your car to shut off.
• A clogged catalytic converter will starve your engine of oxygen it needs for combustion.
• A clogged catalytic converter can cause misfires, poor engine performance, and stalling.
• There are common signs of a failing catalytic converter.
• You can test a failing catalytic converter at home with some simple tools.