Po420 engine code

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P0420 OBD-II Trouble Code Guide: Catalyst System Efficiency Below Threshold (Bank 1)

The short answer is “Yes.”

But before you order a new catalytic converter online, let me give you my disclaimer: This site is for information purposes only. Please consult a qualified professional in your area if you have any questions or concerns about your check engine light.

As I mentioned above, the P0420 code means that your catalyst system efficiency is lower than it should be, as measured by your O2 (oxygen) sensors. This means there may be a problem with either the catalytic converter, the oxygen sensors, or both.

The 02 (oxygen) sensor is designed to monitor the fuel and air mixture in the exhaust to verify that the engine is running efficiently. Your engine control unit (ECU) will use this information to adjust the engine performance as you’re driving. When your O2 sensors are working properly you will get better gas mileage and optimal performance.

After your check engine light comes on and you verify the P0420 error code, there are a few simple steps you can take. First, you should check the entire exhaust system for any visible holes or deterioration.

If the exhaust looks intact you may need to replace the catalytic converter. While it may not be necessary, you could also replace your O2 sensors while you’re under there. That way you don’t have to do it later down the road, if they are in fact damaged.

Sours: https://exhaustsystemsguide.com/p0420-code/

P0420 – Meaning, Causes, Symptoms, & Fixes

Code P0420 Definition

Catalyst system efficiency below threshold (Bank 1).

P0420 catalyst system efficiency below threshold bank 1

What Does P0420 Mean?

The function of thecatalytic converter is to break down harmful pollutants that are created by your vehicle during the combustion cycle and convert them into less harmful gases. Code P0420 indicates that the catalytic converter is not functioning efficiently, therefore increasing the output of harmful pollutants by the vehicle.

What Are the Symptoms of Code P0420?

  • Check Engine Light is on
  • Lack of power from the engine
  • Decreased fuel economy
  • Rotten egg or a sulfur smell

What Is the Cause of P0420?

  • Faulty oxygen sensor
  • Faulty air-fuel sensor
  • Worn or internally failing catalytic converter (Most Common)
  • A leak in the exhaust system
  • Misfire (the root cause of converter failure)
  • Rich or Lean air-fuel ratio (the root cause of converter failure)
  • Leaded Gasoline (the root cause of converter failure)

How Serious Is Code P0420? – Moderate 

While P0420 does not pose a danger to the driver, it can cause driveability concerns such as a lack of power or poor acceleration if left unrepaired. It can also cause severe damage to other components of your vehicle if not addressed in a timely manner. It is recommended that you address P0420 as soon as possible to keep the cost of the repair to a minimum.

Common Diagnosis Mistakes for Code P0420

Often times this code is thought to be a faulty O2 sensor or A/F Sensor; while this is a possibility, the most common problem is a faulty catalytic converter. Do not overlook other codes that are paired along with P0420. Codes like P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308 are misfire codes, and these codes require misfire diagnosis. If the catalytic converter is replaced without repairing the misfire, the new catalytic converter will go bad again. Also, make sure you don’t have codes P0174, P0171, P0172, or P0175 which can mean the engine is running rich or lean, which can burn out your catalytic converter. If these codes or any other codes are present, they should be addressed first.

Tools Needed to Diagnose Code P0420:

How to Diagnose Code P0420:

Difficulty of Diagnosis: 5 out of 5

  1.  Scan your vehicle to verify P0420 is the only code present. If other codes are present, they must be addressed first.
  2. Examine the exhaust system for damage and leaks. Pay close attention to the exhaust manifold, gaskets, and exhaust pipes pre-catalytic converter. If any leaks are found, repair the leak, clear the code, and complete several drive cycles to verify that was the fix.
  3. With the vehicle running and at normal operating temperature, use the digital multimeter to check the voltage reading of the downstream O2 sensor. The downstream O2 sensor produces a relatively steady voltage reading of approximately 0.45V if the catalytic converter is functioning properly. If the voltage of the downstream O2 sensor is constantly jumping between 0.1V and 0.9V, the catalyst is worn and the catalytic converter needs to be replaced.

Estimated Cost of Repair

For error code P0420, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

  • Air fuel sensor or oxygen sensor $200-$300
  • Catalytic converter $400-$2400
  • A leak in exhaust $100-$200 (if welded to repair)

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P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)

Reading Time: 7minutes

There are many issues that could trigger the Check Engine Light to illuminate. However, if you use an OBD-II scanner and get a P0420 code, you may be having issues with your catalytic converter. 

For a full rundown of what this code entails, read on.

What Does the P0420 Code Mean?

Code P0420 stands for “Catalyst System Efficiency Below Threshold (Bank 1).” Put simply, this code indicates that your car’s computer has detected underperformance from the Bank 1 catalytic converter. 

a catalytic converter of a modern car close up view

Bank 1 refers to the side of the engine that houses the number one cylinder. The opposite side of the engine is Bank 2. 

What are the Possible Causes of the P0420 Code?

A faulty catalytic converter is the most frequent cause of  a P0420 trouble code. Issues that can cause this OBD-II code include:

  • A failed catalytic converter (very common)
  • A faulty oxygen sensor (not very common)
  • Circuit problems, such as damaged wiring and loose connections (not very common)
  • An exhaust leak (not very common)
  • Computer issues (e.g., software in need of an update) (not very common)

The catalytic converter can also fail due to a number of other problems. These include engine performance issues, such as a misfire or improper air/fuel ratio, which can cause the converter to overheat.

Loose wiring of a car

Contaminants like coolant and engine oil can also damage the cat.

What are the Common Symptoms of the P0420 Code?

You may notice the following symptoms if you drive a vehicle with a P0420 trouble code:

P0420 typically means that a converter has worn out or degraded—not obstructed or clogged. But if the case is the latter, it can lead to engine performance problems, such as a lack of power, rough idling, and stalling, which are some of the common signs of a clogged catalytic converter. 

How to Diagnose the P0420 Code

There are numerous potential causes for OBD-II code P0420. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the videos below:

How to Fix the P0420 Code

There are multiple reasons why code P0420 might be stored. Therefore, there isn’t a “magic bullet” fix for the issue. You’ll need to diagnose the code accurately, as outlined above, then perform any necessary repairs. Usually the catalyst needs to be replaced, and bolt-on catalysts are available for most vehicles.

The code could be triggered by anything from a bad catalytic converter to a faulty oxygen sensor, so you must do your homework.  

car diagnostic tool for car checkup being used by a mechanic

Also, keep in mind that all vehicles are different. When troubleshooting and repairing diagnostic trouble codes, you should consult the factory repair information for your application. 

Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information. 

What is a Catalyst?

The catalysts on today’s vehicles are “Three Way Catalysts,” meaning that they process three harmful gasses, namely NOx (Oxides of Nitrogen), CO (Carbon Monoxide), and HC (Hydrocarbons, which is unburned fuel)

A “catalyst,” by definition, foments changes in other elements without changing itself – the other elements in this case are the three harmful exhaust gasses.

Inside of a catalytic converter showing a honeycomb design

To treat these exhaust gasses, a catalytic converter has within its shell a fine honeycomb type clay “brick” with thousands of tiny “tunnels” tightly arranged so that the exhaust gas must pass through them as it exits the engine. The walls of these tiny tunnels are meticulously coated with certain precious metals that, as the catalyst reaches operating temperature, will either separate nitrogen and oxygen or add molecules of oxygen, but you can’t do both jobs with the same “brick.” Sometimes both “bricks” are in the same shell – more often, they’re not.

The catalyst brick nearest the engine takes care of the NOx and is referred to as the “light-off cat.” This catalyst has to reach a certain temperature to begin the catalytic process of separating NOx into its nitrogen and oxygen components. This is the only catalyst that is monitored by the ECM/PCM.  

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So why is this process necessary? Well, nitrogen and oxygen naturally bind together in the combustion chamber during high combustion temperatures, such as at road speed and when the vehicle is pulling a load.

In the process of doing its job, the light-off (NOx) catalyst stores oxygen; there is an O2 sensor between the engine and the light-off catalyst, and there is another O2 sensor behind the light-off catalyst but in front of the HC/CO catalyst.

The second catalyst, which is farthest from the engine, handles HC and CO by adding molecules of oxygen and converting them to CO2, which is actually good for the environment, since grass, trees, and flowers need CO2 to thrive.

car electronic engine control unit close look

The O2 sensor between the engine and the light-off catalyst “brick” (that’s the Upstream Sensor) monitors the oxygen level in the exhaust and the ECM/PCM uses that input for Fuel Trim adjustments. 

That Upstream O2 signal switches very rapidly in response to Fuel Trim (several times a second). The O2 sensor behind the light-off catalyst (the Downstream Sensor) is also monitoring oxygen, but if the light-off (NOx) catalyst is storing oxygen properly (meaning the catalyst is healthy), the rear O2 sensor signal will be very lazy when compared to the upstream O2. When the ECM/PCM sees the downstream O2 sensor switching at or near the same rate as the upstream O2 sensor, it sets the P0420 code.

Other Notes About P0420 Code

Make sure that you have ruled out other possible causes of inefficiency in the catalyst system before replacing your O2 sensors or catalytic converter. Some car owners make the mistake of replacing a perfectly fine catalytic converter because of a wiring or software issues. It is best to consult a licensed mechanic to ensure that you get a proper diagnosis so that you don’t waste money on replacing parts unnecessarily.

automotive catalytic converter

P0420 Code FAQs

How do I clear a P0420 code?

You can clear the P0420 code temporarily with a scan tool or code reader. The problem is, the code will come back as soon as your car’s primary computer runs its system self-tests. To get the code to go off and stay off, you’ll need to fix the underlying problem that triggered the code in the first place, then clear the code with a scan tool or code reader.

Can a bad O2 sensor cause a P0420 code?

Yes. A typical catalyst monitor uses the signal from the downstream oxygen sensor to determine catalyst efficiency, and the signal from the upstream sensor is a reference point. As such, failure of either the upstream or downstream oxygen sensor can cause code P0420 to set. The most common cause of the code, however, is a failed catalytic converter.

an oxygen sensor on a catalyst pipe of gasoline engine car close up

What is the p0420 code on a Nissan?

The P0420 code is a generic OBD code with a standard definition from the Society of Automotive Engineers (SAE). SAE refers to the code as “Catalyst System Efficiency Below Threshold (Bank 1)”. But on many newer Nissan vehicles, when using an OEM-level scan tool, the code may come up as “Three-Way Catalyst Malfunction.” In either scenario, the code indicates that your car’s onboard computer perceives a decline in the efficiency of the catalytic converter(s).

How do you test an O2 sensor for a P0420 code?

Most of the time, code P0420 indicates a faulty catalytic converter. There are, however, instances where a bad oxygen sensor can trigger the code.

mechanic conducting diagnostics tests on a vehicle

One way you can rule out the oxygen sensors is by forcing the air/fuel mixture rich and then lean. To force the system rich, carefully add propane to the engine’s air intake (and raise RPMs so the engine doesn’t stall) to enrich the air/fuel mixture. At the same time, monitor the sensors with a scan tool. The sensors should go rich (about 800 mV to 900 mV for a traditional zirconia oxygen sensor) in response to the propane.

You can then force the system lean by disconnecting a large vacuum hose. In this state, the sensors should go lean (around 200 mV-300 mV) for a traditional zirconia oxygen sensor).

If the oxygen sensors respond properly to both the rich and lean conditions, they’re working as they should, and the catalytic converter is likely the cause of the P0420 code.

Products Mentioned in this Guide

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

Keep Reading: Related Posts

File Under : OBD-II Trouble CodesTagged With : catalytic-converter

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Got a p0420 Code? You May Need an Oxygen Sensor Or You May Need Something Else Entirely

When check engine lights are scanned, a p0420 code is a very common result. It’s actually a generic code, meaning it can be thrown from any vehicle after 1996. Commonly, people think the p0420 code indicates that the oxygen sensors need to be replaced, but that’s definitely not always the case.

p0420 Code: Time to Replace an Oxygen Sensor?

Background on Oxygen Sensors

The engine’s fuel injection computer uses oxygen sensors to constantly fine-tune the amount of fuel injected into your engine. Your car will have at least two sensors, and as many as four (unless it’s more than 20 years or so old, in which case it may have only one or none at all). There’s one sensor right ahead of the catalytic converter. This sensor allows the engine computer to constantly adjust the amount of fuel sent to your engine, assuring proper combustion and the best performance and emissions. A second sensor is screwed into the exhaust pipe right past the catalytic converter. This sensor checks the performance of the catalytic converter, making sure it scrubs the last vestiges of pollution from your exhaust.

Oxygen sensors are only a part of a greater system, meaning if the p0420 code (or p0141, or p0135) is thrown, that doesn’t necessarily indicate the oxygen sensors need replacement. Rather, there could be something else in that system does that’s causing the oxygen sensors to appear faulty. This is actually the case with most check engine codes.

Common Causes of a p0420 Code (or Something Similar)

  • Bad Sensor

    Sensors can and do fail, usually just by getting lazier and lazier until the computer doesn’t trust their output anymore. When the computer is slewing the air-fuel ratio up and down multiple times per second and the sensor can’t keep up, there’s a code set, illuminating your check engine light. Occasionally, a sensor can fail outright, often by being poisoned by leaded gasoline (not very common nowadays), or atmospheric chemicals. As you’ll see, it’s a bad idea to simply replace a sensor. It’s wise to check further and see if there’s something wrong that made it fail.

  • Bad Wiring

    Sensors have four fragile wires leading up to them, two for the signal to the computer, and two for a small heating element that helps them get up to their operating temperature more rapidly on a cold startup. Wires that are broken, melted against the hot exhaust pipes, or corroded, will give erratic or missing readings.

  • Bad Spark Plug, Wire, or Fuel Injector

    Any of these can cause one or more cylinders to misfire. Because the oxygen in that cylinder isn’t burned up, the extra oxygen in that cylinder winds up passing over the O2 sensor. This makes the computer think it’s not injecting enough fuel. The danger is that the extra fuel injected to compensate eventually winds up being burned in the catalytic converter. This is rapidly damaging. Similarly, a partially plugged fuel injector (there’s one for every cylinder in your engine) might inject too little fuel into a single cylinder. The computer can become confused about the readings. Any confusion will throw a code and that pesky CHECK ENGINE light as well.

  • Leaky Exhaust Pipes

    A leaky exhaust pipe obviously can let exhaust gases out of the pipe at the leak. But air can also be sucked into the pipe at the same leak. If that leak is upstream of the sensor, it will see the extra oxygen and set a trouble code.

  • Bad Catalytic Converter

    This is a costly repair, but common with a p0420 code. For this reason, we highly recommend a diagnosis prior to performing any replacements.

These are the common things; there are plenty of other, often obscure reasons why an O2 sensor codes might be set.

Now That You Have Some Background, Get to a Mechanic

A trouble code that points to an oxygen sensor (such as p0420, p0135, p0141, or others) is only the first step in your mechanic’s diagnosis of the problem. It turns out that most of the issues that set oxygen sensor codes are not a result of a bad sensor.

So, automatically screwing in a new sensor because there’s a sensor-related code is a big gamble. A good mechanic will always use those trouble codes simply as a starting point in his diagnosis. A good customer that’s done their research (you!) will ask for a diagnosis. Now you know why you shouldn’t just ask for quick replacement of the first part a check engine code points to.

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Sours: https://blog.openbay.com/why-o2-sensor-codes-show-up-in-diagnostic-tests/

Engine code po420

P0420 code definition:

Catalyst System Efficiency Below Threshold (Bank 1)

What the P0420 code means:

A P0420 code indicates a problem with the catalytic converter. The purpose of the catalytic converter is to break down harmful pollutants created during the combustion cycle. By using fine platinum and gold meshes to filter exhaust fumes, the catalytic converter is able to reduce the emissions expelled from the exhaust pipe.

The catalytic converter has two oxygen sensors. One oxygen sensor is positioned in front (upstream) of the catalytic converter and the other O2 sensor is positioned at the rear (downstream).

If the upstream oxygen sensor is working properly, its readings should fluctuate from when the car is at operating temperature and when running in a closed loop. If the downstream oxygen sensor is working properly, and there isn't an issue with the catalytic converter, its readings should remain steady.

When the oxygen sensors have similar readings to each other, it indicates that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases and begins to fluctuate like the upstream oxygen sensor, it means the oxygen levels are too high and the Powertrain Control Module (PCM) will store the P0420 trouble code and turn on the check engine light.

Common causes of the P0420 code?

  • Damaged muffler or leaks in the muffler.
  • Damaged exhaust manifold or leaks in the exhaust manifold.
  • Damaged exhaust pipe or exhaust pipe leaks.
  • A misfire in the engine.
  • Oil contamination in catalytic converter.
  • Faulty catalytic converter (most common).
  • Faulty engine coolant temperature sensor.
  • Faulty front oxygen sensor.
  • Faulty rear oxygen sensor.
  • Damaged oxygen sensor wiring.
  • Oxygen sensor wiring that is not properly connected.
  • Damaged oxygen sensor connectors
  • A leaking fuel injector.
  • High fuel pressure.
  • Use of the wrong kind of fuel (using leaded fuel instead of unleaded fuel)

4 Common symptoms of a P0420 code:

Though there are often no noticeable symptoms of a failure within the catalyst system, including drivability problems, there are 4 common indicators of the P0420 code:

1. Check Engine Light is on. Many things can trigger the check engine light to turn on. A mechanic will need to use a diagnostic tool to read the code and pinpoint the exact cause of the problem.

2. Lack of power after vehicle warms up. The engine will not run as well and may not provide enough power for acceleration.

3. Speed of vehicle may not exceed 30-40 mph. This may cause issues when driving along highways and freeways with higher speed limits, though you may not notice the symptom if you drive slower through mostly-residential areas.

4. Rotten egg smell coming from the exhaust pipe. This smell occurs from the incorrect amount of oxygen in the catalytic converter, which leads to excess sulfur in the fuel tank, creating the odor from the exhaust system.

How does a mechanic diagnose the P0420 code?

  • Uses an OBD-II scanner to retrieve trouble codes stored by the PCM.
  • Views the live data of the downstream (rear) oxygen sensor. The downstream oxygen sensor voltage reading should be steady. Make a determination as to whether the downstream (rear) oxygen sensor is working properly.
  • Diagnoses any other codes that could be causing the P0420 trouble code.
  • Repairs misfires, ignition problems, and/or fuel system problems if necessary.
  • Inspects the rear oxygen sensor for damage and/or excessive wear.
  • Test drives the vehicle while viewing the freeze frame data to determine whether or not the downstream (rear) oxygen sensor is working properly.
  • Checks for available updates of the PCM if the catalytic converter is faulty. After the catalytic converter is replaced, updates to the PCM will be required.

Common mistakes when diagnosing the P0420 code:

The most common mistake is replacing the oxygen sensors before completing the diagnostic process. If another component is causing the P0420 trouble code, replacing the oxygen sensors will not fix the problem.

How serious is the P0420 code?

It is common for a driver to experience no driveability problems when the P0420 trouble code is present. Other than the Check Engine Light being on, the symptoms of this trouble code may go unnoticed. However, if the vehicle is left in error without addressing the problem, serious damage could occur to other components.

Because there are no driveability symptoms associated with the P0420 trouble code, it is not considered serious or dangerous to the driver. However, if the code is not addressed in a timely manner, the catalytic converter could be seriously damaged. Because the catalytic converter is expensive to repair, it is vital the P0420 trouble code is diagnosed and repaired as soon as possible.

What repairs can fix the P0420 code?

  • Replace muffler or repair leaks in the muffler.
  • Replace exhaust manifold or repair leaks in the exhaust manifold
  • Replace exhaust pipe or repair exhaust pipe leaks
  • Replace catalytic converter (most common)
  • Replace engine coolant temperature sensor
  • Replace front or rear oxygen sensor
  • Repair or replace damaged wiring to oxygen sensor(s)
  • Repair or replace oxygen sensor connector(s)
  • Replace or repair fuel injector(s) that are leaking
  • Diagnose any repair any misfiring problems
  • Diagnose and repair any other related trouble codes that have been stored by the Power Control Module (PCM)

Keep in mind:

Problems with the ignition system, fuel system, air intake, and misfires can damage a catalytic converter if they are not addressed quickly. These components are most the common causes of the P0420 trouble code. When replacing a catalytic converter, is it a good idea to replace it with an OEM unit or an oxygen sensor replacement that is of high quality.

It is common for aftermarket oxygen sensors to fail, and when they do, the P0420 trouble code may return again. It is also a good idea to contact the manufacturer to see if your vehicle has a manufacturer warranty on parts that are related to emissions.

Need help with a P0420 code?

YourMechanic offers certified mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-844-668-2785.

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FORD FIX CODE P0420 CATALYST SYSTEM EFFICIENCY ANY FORD

P0420 is a trouble code that gets stored in your car engine’s control module when it recognizes an issue with the catalytic converter’s efficiency.

There are many different reasons why this happens, so you need to know how to diagnose this trouble code correctly to get rid of it. Keep reading, and you will learn everything you have to know about the P0420 code and how to fix it.

Definition

P0420 – Catalyst System Efficiency Below Threshold (Bank 1)

What does the P0420 Code Mean?

Code P0420 indicates the catalytic converter’s efficiency is below the threshold. It can either be caused by a faulty catalytic converter or a false alarm from any of the sensors.

The ECM uses two O2 sensors, one in the front and one in the back of the catalytic converter, to measure efficiency. If the efficiency is low, the P0420 code will be triggered. In most cases, a P0420 code is caused by a bad catalytic converter.

P0420 Symptoms

The most common symptom of code P0420 is a check engine light on the dashboard. In rare cases, you can also notice issues like misfires, higher fuel consumption, or a bad odor smell coming from the exhaust pipe.

However, In most cases, you will most likely notice any symptoms except the check engine light with the P0420 code stored in the engine control unit.

How serious is the P0420 code?

Low – The P0420 code will in most cases not create any further problems with your car’s engine.

The only thing that can happen is that the catalytic converter is so damaged that the catalytic converter parts come loose and blocks the exhaust pipe, which is pretty unlikely to happen.

The P0420 code makes your car’s emissions bad for the environment, though, so you should fix it as soon as possible.

What Is the Causes of P0420?

The most common cause of the P0420 code is a faulty catalytic converter. It can also be caused by a faulty O2 sensor, exhaust leak, intake leak, or wrong placement of the catalytic converter.

It could be a faulty bad catalytic converter, but I have seen many cases when the catalytic converter is pretty new, but it’s not an original OEM part. Some cheaper catalytic converters may not be enough, and in some cases, you have to buy a brand new catalytic converter from the manufacturer.

I have also seen non-OEM catalytic converters that have been installed too far away from the engine on the exhaust pipe. Because of this, the catalytic converter will not get hot enough and will trigger a P0420 code. Here are all possible causes of P0420:

  • Damaged catalytic converter (most common)
  • Not Genuine catalytic converter
  • Wrong placement of the catalytic converter
  • Damaged upstream front O2 sensor / faulty wirings
  • Damaged downstream rear O2 sensor / faulty wirings
  • Exhaust leak
  • Intake leak
  • Oil burn (damaging the catalytic converter)
  • Rich/lean mixture (damaging the catalytic converter)
  • Misfires (damaging the catalytic converter)
  • A faulty engine control unit (rare)

What repairs can fix the P0420 code?

You should first check the function of the catalytic converter with the methods further down in the article before replacing any parts. You will most likely waste your money by just replacing parts, so it is much better to make a proper diagnosis. However, here are some things that can fix the P0420 code:

  • Cleaning the catalytic converter
  • Replace catalytic converter
  • Replace to a genuine original catalytic converter
  • Replace front O2 sensor
  • Replace rear O2 sensor
  • Repair faulty wirings
  • Fix oil burn
  • Fix misfires
  • Fix lean / rich fuel mixture
  • Check the data with an OBD2 scanner
  • Replace engine control unit (rare)

Common P0420 Diagnosis mistakes

The most common mistake is to replace the O2 sensors without doing any proper diagnostics. The cause of this trouble code is most often the catalytic converter – which may get damaged by other problems with your car’s engine like misfires.

Bad O2 Sensors can cause the this trouble code, but is pretty rare.

Common P0420 Code Causes by Car Model

The P0420 trouble code is more common in some car models than others. Here is a list of the most common causes per car brand. These car models are known to have a problem with this trouble code

Remember that these are only general guidelines, and you should be making a proper diagnosis before replacing any parts.

1. Toyota Corolla

The most common cause when you find this trouble code on the Toyota Corolla is a bad catalytic converter. This can often be caused by oil going through the piston rings to get stuck on the catalytic converter if you have a Toyota Corolla that is struggling with the trouble code.

Check for vacuum leaks and exhaust leaks first. Then check to see if you notice any blue smoke coming from the exhaust pipe. If so, it’s a sign that you might want to get expert help to find out where the oil is coming from.  A standard check is to check the crankcase ventilation.

If you do not notice any blue smoke at any RPM, it is most likely your catalytic converter is worn out.

2. Ford Focus

The Ford Focus usually has vacuum leaks or any broken solenoid, which causes a faulty air-fuel mixture and then causes the trouble code.

Check your trouble code memory with a diagnostic scanner to see if you can find any trouble codes about the air-fuel mixture. If everything looks fine, check for exhaust leaks.

Replace the catalytic converter if you can’t find any trouble codes or other problems with the air-fuel mixture.

3. Subaru / Subaru Forester

The Subaru usually has the same problem that the Toyota Corollas have. Check for vacuum leaks or other fuel mixture related trouble codes. Check for any exhaust leaks before the catalytic converter. The most common problem with Subaru engines is the catalytic converter itself.

4. Volkswagen (VW) / Skoda / Seat / Audi A4 1.8T / V6 2.4

These VAG cars have some known problems causing the P0420 code. Check the check valves’ function under the intake and make sure the crankcase ventilation is free from dirt, causing the engine to burn oil, which clogs the catalytic converter.

Check for exhaust leaks around any flex pipes on the exhaust pipe (common cause).

Check for any trouble codes of the O2 sensors. If no problems were found, replace the catalytic converter. It’s a widespread problem on both the 1.8T and the V6 petrol engines.

The 1.8T catalytic converter can be pretty difficult to replace if you do not have a lot of experience. The V6 has two catalytic converters, ensuring you troubleshoot and replace the catalytic converter on the right bank.

How to Diagnose code P0420

P0420 Check Engine Light

The P0420 Code is mostly caused by a faulty catalytic converter as mentioned before. You should always diagnose it properly with the methods down below before replacing anything.

However, you can clean the catalytic converter by using an additive in the fuel tank in some cases. There are many different additives on the market, so we recommend choosing one of the best catalytic cleaners from our list.

  1. Connect an OBD2 Scanner and look for related trouble codes. Repair any related trouble codes regarding ignition or fuel before you try to fix the code.
  2. Check the live data to see the front and read O2 sensor signals. The car engine should be scorching – and the front sensor should fluctuate between 0-1 volts, and the rear should be steady at 0.7 – 0.9 volt. If it is not, there is a risk that the catalytic converter is defective.
  3. Heat the engine and check the temperature at the front of the catalytic converter and then in the rear. If the engine is hot and there is no difference in temperature before and after the catalytic converter – your catalytic converter does probably not work.
  4. If the catalytic converter is installed easily, it can be worth removing the pipe from one end of it and check inside the catalytic converter for any visual damages.
  5. If everything points at a faulty catalytic converter – replace it. If you can’t find any problem with the temperature, voltage, or a visual inspection, you should try to repair other related trouble codes and then clear the codes and try again.
  6. If you still can’t find any problems. Make sure it is a genuine OEM catalytic converter, and it is installed in the original place. If everything seems fine – replace the catalytic converter.

Check out this video for more advanced P0420 Diagnosis.

Catalytic Converter Damaged Causes

There are a few things that are known for damaging the catalytic converter, which can cause the trouble code; here are the most common:

  • Misfires
  • Oil consumption
  • Exhaust leak
  • Intake leak
  • Rich mixture
  • Lean mixture
  • Bad ECM/PCM[/su_tab]

Important Note:

Many things could cause the O2 sensors or the catalytic converter to fail. You have to make sure that you fix these problems before you replace any parts, or they may get be damaged again. Check your DTC memory to find a combination of any other trouble codes.

Fix them before this trouble code. Ensure that your car is not burning any oil by checking the exhaust smoke, Blue Smoke = Oil, White = Water, Gray/Black = Rich Mixture.

Estimated Repair Cost

The estimated cost of repairing the code is the following. The prices are including parts and labor work at a workshop. The costs do not include diagnosis costs.

  • Catalytic Converter Replacement – 500$ to 1500$
  • Front O2 Sensor Replacement – 150$ to 300$
  • Rear O2 Sensor Replacement – 150$ to 300$

Can I remove any parts to get rid of the P0420 code?

You cannot just remove any parts to fix this trouble code. It will most likely give you another trouble code or some other symptoms. You can reprogram the engine control unit to take away the catalytic converter monitoring. Still, it’s not recommended because, in most countries, there is a law that you should have your catalytic converter function working.

If you want to reprogram the function, you can also delete the catalytic converter. Remember that if you remove the catalytic converter, you will most likely not pass any emission tests.

There is another way to trick the engine control unit by replacing the rear oxygen sensor in a pipe. This method can work if you desperately want to get rid of the P0420 code, but it’s not a recommended method, and it may get you into trouble.

If you’re going to check the price and more information about this tool, you can check it out here on Amazon: O2 sensor adaptor. Remember to check the laws in your state or country before installing one of these.

Common P0420 Related Questions

How to fix the P0420 code?

To fix the P0420 code, you need to diagnose what is causing the trouble code. Start with inspecting and diagnosing your catalytic converter and continue with checking the O2 sensors.

What can cause a P0420 code?

A bad catalytic converter is the most common cause of the p0420 code. This doesn’t mean that you should replace it, though. Always do proper research before replacing parts to save money.

What does code P0420 Bank 1 mean?

The P0420 code means that rear O2 sensors report to the engine control module that the catalytic converter is not doing it’s job properly. The rear O2 sensor is comparing the signal from the front O2 sensor.

How to clear code P0420?

To clear the P0420 code you need to use an OBD2 scanner. Remember that just clearing the P0420 code will most likely solve the problem, you do also have to fix the problem.

How much does it cost to fix a P0420 code?

There is no fixed price to fix the P0420 code. However, it is often caused by a faulty catalytic converter, and one of these usually costs 500$ to 1000$ for the part and 100$ – 200$ in replacement cost.

Can I drive with the P0420 code?

The P0420 code itself is not causing any serious damages to your vehicle for short distances. However, driving long distances and ignoring the trouble code is not recommended. Fix it as soon as possible.

Sours: https://mechanicbase.com/trouble-code/p0420/

Now discussing:

P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1)

P0420 code definition

Catalyst System Efficiency Below Threshold (Bank 1)

What the P0420 code means

The purpose of the catalytic converter is to break down harmful pollutants that are created during the combustion cycle. By using fine platinum and gold meshes to filter exhaust fumes, the catalytic converter is able to reduce the emissions expelled from the exhaust pipe.

The catalytic converter has two oxygen sensors. One oxygen sensor is positioned in front (upstream) of the catalytic converter and the other oxygen sensor is positioned at the rear (downstream).

If the upstream oxygen sensor is working properly, its readings should fluctuate from when the car is at operating temperature and when running in a closed loop. If the downstream oxygen sensor is working properly, and there isn't an issue with the catalytic converter, its readings should remain steady.

When the oxygen sensors have readings that are similar to each other, it is an indication that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases, and begins to fluctuate like the upstream oxygen sensor, it means that the oxygen levels are too high and the Powertrain Control Module (PCM) will store the P0420 trouble code.

What causes the P0420 code?

  • Damaged muffler or leaks in the muffler
  • Damaged exhaust manifold or leaks in the exhaust manifold
  • Damaged exhaust pipe or exhaust pipe leaks
  • A misfire in the engine
  • Oil contamination in catalytic converter
  • Faulty catalytic converter (most common)
  • Faulty engine coolant temperature sensor
  • Faulty front oxygen sensor
  • Faulty rear oxygen sensor
  • Damaged oxygen sensor wiring
  • Oxygen sensor wiring that is not properly connected
  • Damaged oxygen sensor connectors
  • A fuel injector that is leaking
  • Fuel pressure that is high
  • Use of the wrong kind of fuel (using leaded fuel instead of unleaded fuel)

What are the symptoms of the P0420 code?

How does a mechanic diagnose the P0420 code?

  • Uses an OBD-II scanner to retrieve trouble codes stored by the PCM.

  • Views the live data of the downstream (rear) oxygen sensor. The downstream oxygen sensor voltage reading should be steady. Make a determination as to whether the downstream (rear) oxygen sensor is working properly.

  • Diagnoses any other codes that could be causing the P0420 trouble code.

  • Repairs misfires, ignition problems, and/or fuel system problems if necessary

  • Inspects the rear oxygen sensor for damage and/or excessive wear

  • Test drives the vehicle while viewing the freeze frame data to determine whether or not the downstream (rear) oxygen sensor is working properly.

  • Checks for available updates of the PCM if the catalytic converter is faulty. After the catalytic converter is replaced, updates to the PCM will be required.

Common mistakes when diagnosing the P0420 code

The most common mistake is replacing the oxygen sensors before completing the diagnostic process. If another component is causing the P0420 trouble code, replacing the oxygen sensors will not fix the problem.

How serious is the P0420 code?

It is common for a driver to experience no driveability problems when the P0420 trouble code is present. Other than the Check Engine Light being on, the symptoms of this trouble code may go unnoticed. However, if the vehicle is left in error without addressing the problem, serious damage could be caused to other components.

Because there are no driveability issue symptoms associated with the P0420 trouble code, it is not considered serious or dangerous to the driver. However, if the code is not addressed in a timely manner, the catalytic converter could be seriously damaged. Because the catalytic converter is expensive to repair, it is vital that the P0420 trouble code is diagnosed and repaired as soon as possible.

What repairs can fix the P0420 code?

Additional comments for consideration regarding the P0420 code

Problems with the ignition system, fuel system, air intake, and misfires can damage a catalytic converter if they are not addressed quickly. These components are most the common cause of the P0420 trouble code. When replacing a catalytic converter, is it a good idea to replace it with an OEM unit or an oxygen sensor replacement that is of high quality.

It is common for aftermarket oxygen sensors to fail, and when they do, the P0420 trouble code may return again. It is also a good idea to contact the manufacturer to see if your vehicle has a manufacturer warranty on parts that are related to emissions.

Need help with a P0420 code?

YourMechanic offers certified mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

This article originally appeared on YourMechanic.com as P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1).


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