What Is A P0420 Code?

Engine code

A P0420 code on your car’s check engine light could mean one of two things:

  • a problem with the catalytic converter
  • an issue with the O2 sensor on your vehicle’s exhaust system.

Both can cause problems for your vehicle and will require some attention from an auto mechanic. Here’s how to recognize a P0420 code and what you should do about it.

What Is A P0420 Code?

P0420 means that the oxygen levels are below the usual threshold. It is most often the result of problems with your car’s exhaust or fuel systems. Unfortunately, most of the time, a P0420 is difficult to diagnose.

The catalytic converter is part of the exhaust system. It helps clean up the exhaust gas by combining any remaining unburned fuel and carbon monoxide with the exhaust. This chemical agent can also break down nitrogen oxides into nitrogen. It helps clean the exhaust gas from toxic pollutants.

The converter has two oxygen sensors. One on the upstream side. The other one is on the downstream side. These 2 sensors measure the oxygen and compare the results. If these sensors indicate the same things, it is clear that something is wrong. At this point, the Powertrain Control Module emits the P0420 code, prompting the check engine light to turn on and informing you that there is a catalyst problem.

The best advice is simply to call a mechanic to diagnose the problem and solve it.

How Serious Is A P0420 Code?

A P0420 code also called a catalytic converter malfunction, occurs when part of your engine’s emissions system experiences problems.

Essentially, it monitors and controls your engine’s performance and determines when you need to make changes in order to save fuel.

The code doesn’t necessarily mean that you need immediate repairs.

However, there are a few warning signs to look out for. If your check engine light is on or flashing at any time while driving, it would be a safe decision to pull over safely as soon as possible and call a mechanic right away.

What Are The Causes Of The P0420 Code?

As the most common cause of a P0420 code is a faulty catalytic converter, the following are some other potential causes:

  • Misfiring engine
  • Exhaust manifold damage or leakage
  • High fuel pressure
  • Loose connection in the Oxygen wiring
  • Irregular engine coolant temperature sensor
  • Exhaust pipe damage or leakage
  • Catalytic converter oil contamination
  • A faulty rear or front oxygen sensor
  • Oxygen wiring damage
  • Fuel injector leakage
  • Filling your vehicle with the wrong fuel type 

Can I Still Drive With A P0420 Code?

A P0420 OBD-II error means that something is wrong with your vehicle’s catalytic converter

 This may seem like a scary problem, but in all likelihood, you can drive your car with no problems.  Your catalytic converter is an emissions control device, so it helps reduce pollution.

However, when it malfunctions or breaks down completely, it will send a check engine light to alert you of its failure.

You might notice some performance issues as well as increased fuel consumption if your cat isn’t working properly. It could also make your engine run hotter than normal and trigger a check engine light for other reasons (such as low oil pressure). In most cases, you can continue driving until you have time to get it fixed by a professional mechanic or at an auto shop near you.

Can The P0420 Code Cause A Misfire?

Yes, it could cause a misfire. That’s why it is recommended to stop as early as possible.

How To Fix A P0420 Code?

The first step is figuring out what the P0420 code actually means. Most service professionals will use an OBD-II scanner to find out the code the Power Control Module (PCM) is displaying.

When the voltage from the downstream oxygen sensor fluctuates the same way as the upstream oxygen sensor, it is a clear sign that the oxygen levels are too high and the Powertrain Control Module will activate the P0420 code.

A mechanic will first make sure the pump for the upstream and downstream oxygen sensors are doing what they should be doing. If there are no malfunctions with those two parts, then the mechanic will next go on to check for possible misfires, fuel delivery problems, and more. It’s also a possibility that the mechanic will also check the rear O2 sensor to gauge any potential wear and tear.

How Much Does It Cost To Fix P0420?

The cost to fix a P0420 error varies depending on what type of vehicle you have. For example, if you have an older car or truck and your check engine light comes on as soon as you start your car, it’s likely that repairing the problem will be inexpensive because most auto parts stores carry generic replacements for such old parts.

However, if your check engine light comes on for something more complex or with newer technology like in today’s cars and trucks, fixing it may be expensive because generic replacements won’t work. An easy way to find out how much it’ll cost to fix your car’s check engine light is to call around locally and ask different auto repair shops what they charge for similar repairs.

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