Will a Bad Catalytic Converter Throw a Code?

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For any vehicle owner or driver, it’s essential to be mindful of identifying a faulty catalytic converter. DTC codes are recognized across the world for this purpose. But, will a bad catalytic converter throw a code? Yes, a bad catalytic converter will usually give rise to DTC code P0420 and the Check Engine Light (CEL) will be blinking. 

Catalytic converters are prone to failure; unfortunately, these high-ticket replacement parts are costly as well. That’s why It’s important to thoroughly diagnose a faulty catalytic converter so that it is possible to sidestep spending money and time in line with the functional part. 

In this article, we’ll cover all information about a bad catalytic converter and its replacements. In this article, we will explain everything you need to know related to a faulty catalytic converter and its corresponding DTC code. 

What is a Catalytic Converter?

catalytic converter

A catalytic converter is a vital component of vehicles that uses an enclosed chamber called the catalyst to switch around poisonous gases from the motor’s emissions into non-toxic gases, such as steam. 

The work of the catalytic converter is to break up the harmful molecules in the emissions before those emissions are released into the air. It is located beneath the car and resembles a large box. There are two pipes connecting it to the engine that feeds into it.

Will a Bad Catalytic Converter Throw a Code?

bad catalytic Converters

In general, a catalytic converter reduces the number of fumes in the air that could directly affect the people and environment, resetting 90 percent of all harmful emissions to lesser peaks. To achieve maximum energy efficiency, the catalytic converter is positioned in the exhaust path between the engine and the muffler. 

However, the efficiency level of catalytic converters can vary depending on the specific requirement of the pollution control board of different states. Technically, a bad catalytic converter means it’s no longer able to reach that specific efficiency level. 

When this happens, the CEL will blink as the computer system will receive a signal from oxygen sensors placed around the catalytic converter (unless they’re faulty). At that time, you’ll notice your On-Board Computer system is showing the DTC code P0420. 

Read also: Can You Drive With A p0299 Code?

What Does The P0420 Code Mean?

Well, you have seen the DTC code “P0420”. Now you might be wondering what this code actually means by this code, right? Let’s break it down. A DTC code P0420 stands for “Catalyst System Efficiency Below Threshold (Bank 1)”. 

As stated above, the DTC code P0420 appears when catalytic converter efficiency is low. This code indicates that Oxygen sensor input oxygen levels are lower than the specific threshold (Bank 1). 

Generally, the lower oxygen conditions are caused by faulty exhaust or fuel systems.  However, there are some other causes that may trigger the DTC code P0420. These include:

  • Contamination in catalytic converter’s oil
  • Damaged exhaust pipe or leakage
  • Faulty air-fuel sensor
  • Oxygen wiring damage
  • High fuel pressure
  • Fuel injector leakage
  • Misfiring engine

Symptoms of A Bad Catalytic Converter

Imagine your vehicle’s oxygen sensor is faulty, and you’re not aware of this, how do you do if your catalytic converter is bad? Don’t be hopeless, there are some common symptoms that indicate a catalytic converter is malfunctioning. So, what are the symptoms of a bad catalytic converter? Check them below:

Sluggish Acceleration

Among the most common symptoms of a faulty catalytic converter is a loss in engine performance due to car deceleration. Vehicles often use catalytic converters prompted primarily by concern about excessive automotive emissions created by unburned fuel. 

When the honeycomb design gets clogged with carbon or its interior melts due to excessive heat, the catalytic converter can become partially or completely obstructed. 

Dependable exhaust flow is necessary for the engine to operate at its maximum output. If the flow is severely restricted by a clogged converter, your motor will make less power when accelerating, climbing a hill, or towing a heavy load. With the help of a cleaning kit to remove carbon buildup, you can remove a converter clog.

Strange Noise

When components of the catalytic converter break down due to the automotive racing on the track, loud noises might be produced from underneath your vehicle running or idling. This noise is typically the loudest when you first get in the vehicle.

It’s imperative not to mention that pieces of the catalytic converter’s honeycomb that can drift farther down the exhaust manifold can be accessed via the car’s tailpipe. This blockage could be frequent enough to cause the car to stall and even prevent the ignition from being started up again.

Emissions Above the Limit

The increased carbon emission level due to the filtration system of your car’s exhaust system indicates that your converter has failed. If you observe a virtually unchanged output of exhaust gas from your vehicle’s exhaust after the upgrade, then the catalytic converter may still be functioning properly. 

Recalling to have the converter swapped out could be important to preserve the performance of your automobile. It’s worth mentioning that the vast majority of areas in the United States demand for your vehicle to have smog testing every few years. One of the most common causes for failing a smog test is a bad catalytic converter.

Increased Fuel Consumption

With less airflow to your catalytic converter, than your unit is designed to handle, your car may burn more fuel than usual. Because the reduced acceleration symptom shares its base case, the lower airflow also compromises your gas pedal’s responsiveness.  

That signifies that the mixture is richer than it needs to be, suggesting that a faulty fuel filter might be causing a decrease in MPG. Since a drop in gas mileage is typically caused by other issues, any issues ought to be inspected before being ruled out. 

But much of the time, a decrease in the engine’s power in combination with other symptoms could be a sign that the converter needs to be changed.


How do you diagnose a bad catalytic converter?

With as much as the vast majority of testers will need, removing just the oxygen sensor or loosening the exhaust line summed upwind of the catalytic converter should be the simplest test. If the misdiagnosis disappears with this simple step, you probably have insight into the issue.

Can a bad o2 sensor cause catalytic converter failure?

The oxygen sensor may damage the catalytic converter, although the damage is not immediate. The danger of damage to the computer chip, which actually happens, is the oxygen sensor malfunctioning and sending out incorrect information.

Can a bad catalytic converter ruin your engine?

The typical catalytic converter is prone to overheating and can damage your vehicle’s engine. You must always do your best to rectify a malfunction in your automobile’s engine if you see a misfire. If the malfunction is caused by a problem with the catalytic converter, discuss the issue with a repair specialist.

Final Words

So, what do you think? Will a bad catalytic converter throw a code? You have already got the answer, right? However, a bad catalytic converter can be caused due to other issues in your car’s exhaust system. So, whether you see the DTC code or not, as soon as you encounter any of the symptoms we mentioned above, take your vehicle to a mechanic immediately.

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