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P0420 Code: What It Is and How to Fix It

  • Car Care Tips
  • Renee Martin
  • 14 minutes

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A P0420 code indicates that your vehicle’s computer (PCM) has detected a problem with the catalytic converter. The catalytic converter’s function is to break down dangerous pollutants produced during the combustion cycle, lowering emissions released through the exhaust pipe. While this code poses no hazard to the driver, they should fix it as soon as possible to avoid more issues, including a failed emissions test. 

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What is a P0420 code? 

The P0420 code is a diagnostic trouble code (DTC) means your car’s catalyst system is not working as well as it should, i.e., below the threshold. This could be because of problems with the car’s fuel or exhaust systems.

The P0420 error number indicates a low catalyst system efficiency. This is usually caused by issues with your vehicle’s exhaust or fuel systems. It can be difficult to diagnose at times. 

A car’s catalytic converter is a part of its exhaust system. It functions by converting the unburned fuel and carbon monoxide (CO) from the combustion process into carbon dioxide (CO2) and water (H2O). It also converts NOx (nitrogen oxides) to nitrogen. 

p0240 catalytic converter trouble

The converter employs two oxygen sensors, one upstream and one downstream. If these sensors produce comparable results, something is wrong. When the Powertrain Control Module (PCM) triggers the P0420 code, the check engine light illuminates, alerting you to a catalyst problem. 

Do note that several more circumstances could result in fault P0420. However, the code usually indicates a problem with the catalyst/emissions system. 

How serious is engine fault code P0420? 

Engine fault P0420 isn’t frequently a threat to driving safety. The defect is unlikely to cause serious drivability or reliability issues. However, your engine may be emitting more dangerous pollutants because the catalyst system on bank 1 is underperforming. As a result of this coupled with the check engine light, you are unlikely to pass emissions inspections. 

Like with any engine problem, the safest option is to diagnose and repair the P0420 problem as quickly as feasible. So we’re not suggesting that you overlook these difficulties for weeks or months. Rather, it’s probably safe to keep driving with engine code P0420. Use your best judgment. Play it safe if the automobile feels risky or if there are other engine codes, major symptoms, etc. 

Can you still drive with P0420? 

Yes, it is safe to drive with P0420 present in most instances. Aside from the check engine light blinking, a person may not notice any substantial changes in how a car performs. 

For example, if you detect the engine running lean, it’s advisable not to drive it or, at the very least, keep the throttle input and RPMs low. Lean engine operation may put the engine in danger of more significant issues. Driving with insufficient power and other drivability difficulties might also endanger one’s safety. 

You’ll find more info on can you drive a car without a catalytic converter?

How to diagnose code P0420 

Here’s a quick rundown of how to troubleshoot and diagnose the P0420 engine code: 

  • First off, make sure that P0420 is the only engine code present. 
  • Clear the code and drive for approximately 15 minutes. Check to see if the code is returned. If not, repeat the process a few times to be sure. If DTC P0420 appears, there is a genuine problem. 
  • Examine the exhaust system physically for any damage, holes, rust, or other potential leaks. Don’t forget about the exhaust manifold, a common source of leaks. 
  • Examine the voltage value from the O2 sensor. On most engines, standard readings should be about 0.4 to 0.5 volts. If it’s dramatically off or bouncing about, it’s most likely due to a problem with the catalytic converter. 
  • Engines occasionally experience minor problems, and fault codes occur at random. In these circumstances, just clearing and deleting the code may be sufficient to resolve the issue. Otherwise, it’s time to figure out what’s triggering DTC P0420. The techniques outlined above are fairly successful for exhaust leaks and cat failure. However, if you’re receiving additional engine codes, you’ll need to be a little more creative and problem-solving. 

What are the signs of a P0420 code? 

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The first and most common sign of a P0420 code is the activation of your check engine light. Second, your engine will not operate as smoothly as usual, which may prevent you from exceeding 30 to 40 mph.  

This is due to a decrease in engine power output. You may also detect a rotten egg odor coming from the exhaust. This also occurs when the catalytic converter is used in excess or outside normal driving conditions. 

What are some possible causes of a P0420? 

A malfunctioning catalytic converter is the usual suspect for a P0420 code. 

Some more possible causes are: 

  • Damage to or leakage from the exhaust manifold 
  • Damage or leaking in the exhaust pipe 
  • Engine misfire 
  • Contamination of catalytic converter oil 
  • Sensor for engine coolant temperature that isn’t working properly 
  • A malfunctioning oxygen sensor in the back or front 
  • Damage to the oxygen wiring 
  • The O2 wiring has a loose connection
  • Leaking fuel injectors
  • Excessive fuel pressure 
  • Using the incorrect gasoline type in your car (i.e., leaded instead of unleaded fuel) 

How hard is it to examine a P0420 Code? 

Before you begin any repairs, you must correctly diagnose the P0420 error code. Most service technicians will use an OBD-II scanner to acquire the specific code displayed by the Power Control Module (PCM). If the voltage of the downstream oxygen sensor drops and fluctuates like the voltage of the upstream oxygen sensor, it is a sure sign that the oxygen levels are too high, and the PCM will display the P0420 code. 

P0420 Code

However, if there are no evident abnormalities with the upstream and downstream oxygen readings, the mechanic will check for engine misfires, ignition problems, and even faults in the fuel system. The mechanic may also inspect the rear O2 sensor for excessive wear or damage. 

An expert will test drive the vehicle and monitor the freeze-frame data. This enables them to establish whether or not the back O2 sensor is functioning properly. Finally, we recommend updating the PCM to the most recent version in case something is wrong with it. It’s not uncommon for an out-of-date PCM to be the source of your vehicle’s problems. 

How much does DTC P0420 repair cost? 

The cost of repairing DTC P0420 varies greatly depending on the diagnosis. If it’s just a minor exhaust leak, you might be able to weld the holes yourself for next to nothing. Catalytic converters, on the other hand, can be costly. Essentially, P0420 repairs might cost anywhere from $10 to $2,000 or more. 

Can I repair the P0420 engine code at home? 

You certainly can repair the P0420 engine code at home. But there’s a hitch -it is absolutely essential to correctly diagnose the problem before proceeding with any modifications. Depending on the source of the problem, you may need to: 

  • Change the catalytic converter. 
  • Replace one or both O2 sensors. 
  • Replace the wiring or connectors for the O2 sensor. 

You may also need to repair or replace the muffler, update the software on your car, or replace any leaking exhaust system components. If you’re unsure what repairs your automobile requires, take it to a professional for a comprehensive diagnostic inspection and repairs. 

How expensive are catalytic converters? 

They can be quite pricey. Platinum, palladium, and rhodium are some expensive metals found in catalytic converters. All of them are high-priced materials that result in a high-priced catalytic converter. New ones can cost anything from $500 to $2,000 or more. You can find used ones for as little as a couple of hundred dollars, but be wary of possible faulty parts. 

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How do I fix the error code P0420? 

P0420 is a typical error code caused by exhaust leakage. First, examine the exhaust system for evident damage. Welding could be a simple and inexpensive solution. However, if your exhaust is in bad general condition, it will most likely only be a temporary repair. After that, it could come down to the necessity for a new exhaust system, exhaust manifold, etc. 

Here’s a step-by-step guide to fix the P0420 error code

Step 1 – Fix other codes

First, resolve any other codes that may have come up besides the P0420; especially troublesome is the P0300 series of cylinder misfire codes. A P0300 code could be related to something in the ignition (spark plug or coil), the fuel injector, compression, or fuel contamination.

Step 2- Check for and resolve exhaust system leaks

Pressurize the exhaust system with compressed air and spray soapy water around suspected areas. Once identified, fix it using exhaust tape, epoxy, gasket replacement, tightening loose bolt/s, or cutting a portion out and joining it together with new pipe and clamps.

Step 3- Check for cylinder imbalance

If one cylinder is running lean and the other cylinders are running rich, this is an indication that the engine has an imbalance in power output. This imbalance can create excessive emissions by raising hydrocarbon and nitrous oxide output simultaneously. Most advanced diagnostic scan tools are capable of running a cylinder imbalance test, but another way to check for cylinder imbalance is to scope the ignition pattern. In general, cylinders with short burn lines indicate lean cylinders.

Step 4- Check your spark plugs

Another cause of elevated emissions is worn-out or faulty spark plugs.  To meet stringent emission durability requirements of 80,000 or more miles, many modern vehicles come equipped with long-lasting iridium spark plugs. These long-lasting iridium spark plugs sometimes get replaced with spark plugs made of other materials and may not provide the same length of service life. As the spark plug starts to fail, emissions can increase.

While on this, make sure to clean your catalytic converter efficiently.

What does code P0420 mean on Honda?

The P0420 Honda indicates an issue with the catalytic converter’s efficiency. Engine misfires, defective oxygen sensors, or fuel system problems can lead the code to activate.

How do you fix code P0420 on the Honda Accord?

Here are some steps to fix a P0420 code Honda Accord.

  • First, remove the O2 sensor and pour 4-6 ounces of seafoam into the opening, replace the sensor, and leave it overnight. Reset the code and then continue driving.
  • Increase the gap between the oxygen sensor and the converter using a spark plug non-fowler.
  • The most typical fix for the error code is to replace the catalytic converter.
  • If required, replace the oxygen sensors. But it won’t always be the case.
  • Replace the oxygen sensor’s wire or connectors.
  • Then, clean the catalytic converter.
  • Change the air intake hose.

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What does error code P0420 mean on Nissan?

P0420 code Nissan implies that the PCM has detected a fault with the catalytic converter’s Bank 1.

How do I fix my Nissan P0420 code?

Here are some steps you can follow to fix a P0420 code Nissan.

  • Examine the exhaust and ensure there are no leaks. You can locate the upstream oxygen before the catalytic converter.
  • Use a spark plug non-fowler to create space between the O2 sensor and the catalytic converter.
  • Then, clean the catalytic converter. Reduce the gasoline level to one-quarter of a tank. Fill the gas tank with the cleaner. Drive the car for 150 miles or run the engine for 30 minutes at around 200 rpm.
  • Do a replacement for the catalytic converter.
  • Replace one or both O2 sensors as required.
  • If needed, replace the O2 sensor’s wire or connectors.

What does P0420 code Chevy imply?

This error code implies a low catalyst system efficiency. This code indicates that oxygen levels are below the recommended threshold in Bank 1, usually caused by car exhaust or fuel system issues.

What does code P0420 Bank 1 mean on Toyota Camry?

P0420 code Toyota Camry means that the catalytic converter is not working correctly. The code relates to the oxygen (O2) sensors on the Bank 1 side of the exhaust system before and after the catalytic converter.

Does P0420 mean I need a new catalytic converter?

The code indicates that a converter has degraded or worn out rather than getting clogged. But if it is clogged, it can cause engine performance issues like stalling, lack of power, and rough idling.

Why am I still getting a P0420 code after I replaced my catalytic converter?

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Replacing a catalytic converter may not resolve this error code. The following may be the reasons for that.

  • You should reset the check engine light.
  • The shop may have replaced only one catalytic converter, but the second one also needs replacement.
  • The car injects too much fuel, causing damage to the catalytic converter or confusing the O2 sensors.
  • There is an exhaust leak inside or near the catalytic converter.
  • The replacement catalytic converter is faulty or of the incorrect type.
  • There is an issue with the wiring for the catalytic monitor sensor or the PCM.
  • The O2 sensor is defective.
  • There’s oil contamination due to a defective engine.

Which O2 sensor causes P0420?

P0420 code turns on when the upstream and downstream oxygen sensors detect that the catalytic converter is malfunctioning. Essentially, the downstream sensor identifies that some oxygen entering the converter is not getting burned.

Can P0420 cause a car not to start?

The PCM will record the P0420 code and may cause your car not to start. It is because the voltage of the downstream oxygen sensor drops and begins to vary like the upstream oxygen sensor when the oxygen levels are very high.

Can bad spark plugs cause P0420?

When the error code activates, it signifies either a problem with the oxygen sensors or a problem with the catalytic converter that decreases efficiency. So, a defective plug may be enabling unburned fuel to enter the converter and causing damage to it over time.

Can dirty fuel injectors cause P0420?

A false P0420 code may activate if defective fuel injectors in one or more cylinders are affecting the combustion. Then, replace the joint fuel pipe and fuel injector sets.

How long does it take for P0420 to reset?

The car’s PCM will reset the code after a fixed interval, during which it rechecks all of its sensors. After around 10-20 cycles, the reset may occur automatically. A cycle is a phase in which you turn on the ignition and turn it off.

Here’s a video to help you understand more about the P0420 code:

What can cause a false P0420 code?

The following can lead to a false engine error code.

  • Wire damage: Oxygen sensor wires can send a misleading reading to the PCM.
  • Defective oxygen sensors: Typically, two oxygen sensors are located before (upstream) and after (downstream) the catalytic converter. A defective oxygen sensor can result in a fault P0420 code.
  • Leak in exhaust: The code can appear due to a loose or damaged sensor connection, an exhaust leak, or faulty O2 sensors.
  • A leak from a fuel injector: The code can appear due to the high fuel pressure or incorrect fuel type.
  • Oil usage: The code can activate if your vehicle is utilizing oil.
  • Code not cleared: The code may not have been cleared and remains in memory after resolving the issue.
  • Prior O2 sensor failure: The false code will be due to another defective O2 sensor that was repaired.

FAQs

What does code P0420 Bank 1 mean?

The P0420 code Bank 1 means the catalyst system efficiency is less than the threshold for Bank 1. The code appears when the onboard computer identifies that the catalytic converter’s Bank 1 is not working properly.

What is the most common cause for a P0420 code?

The most common reason for the code to appear is that the car’s catalytic converter isn’t working effectively. To function properly, the emissions entering the catalytic converter must be completely balanced and not much increased.

Is the P0420 code a catalytic converter or an O2 sensor?

If this error code appears in your car, it will be because your car’s catalytic converter isn’t working correctly.

Finding the right coverage and refinance for your car 

In situations like these, you might wonder if your auto insurance covers catalytic converters or catalytic converter thefts. Way.com can help keep your auto insurance expenses low while giving you the coverage you need.  What’s more, there’s no need to fill out forms or visit an insurance office. Just download the Way.com app, answer a few questions, and let us take care of it.

Now that you have studied the details of the P0420 code and fixed your car’s performance issues, you can now focus on another important part of your automotive journey – auto refinancing. Our hassle-free approach to auto refinancing can help you achieve your auto-related goals faster! 

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