The OBD-II code system is designed to help in diagnosing problems in the car. That is done with the help of fault codes that are categorized for every car system. The P0420 error code is one of those codes that most often cause headaches to drivers. But what indicates a P0420, and do you need to worry?
A P0420 error code is related to the problems with the catalytic (CAT) converter. The exact message that is coming with this error is “Catalyst system efficiency below threshold (Bank 1). That means that the catalytic converter efficiency is low. The cause of this issue is usually an old and worn converter. But, other problems can inflict it, like an engine misfire, an exhaust leak, or a faulty oxygen sensor.
Diagnosing a P0420 can be difficult, so we recommend you read the rest of the article. We will explain the symptoms that go with this error, what can be the underlying cause for it, and how to resolve it.
Understanding the P0420 OBD2 Code: What Does It Mean?
A Deep Dive into OBD-II Codes
OBD-II codes are a unified diagnostic system that is used in all cars made in the United States after 1996. Before the OBD system attempts were to make car diagnostics easy, but only after this system came to life, did it become possible.
Different systems and components in the vehicle have sensors that monitor how they work. All this information goes through to the electronic control module (ECM), where they are processed. If the ECM detects values that are not in the predefined range, it will signal a problem. The ECM will detect which system is in problem and thus release the right error.
This makes diagnosing the error much simpler. The mechanic needs to know what can cause a particular error and to check these systems—that way the problem is diagnosed and fixed easier and faster.
The Role of the Catalytic Converter
A catalytic converter is a part of the exhaust system. Its role is to lower the level of bad emissions that would end up in the atmosphere. This is done by exposing the exhaust fumes to the metals and chemicals in the catalytic (CAT) converter. There, the carbon monoxide (CO) from the combustion process is converted into carbon dioxide (CO2) and water (H2O).
Oxygen (O2) sensors control the work of the CAT converter. They measure the percentage of oxygen in the exhaust gases. Depending on the type of vehicle, there can be a different number of oxygen sensors installed. Today, most vehicles have 4 oxygen sensors. One is located before the CAT converter, and one is on each exhaust manifold.
Interpreting the P0420 Code
If the O2 sensors detect similar results, then something is not right. The values of oxygen have to be different upstream and downstream from the converter. If not, the O2 sensor sends this information to the ECU, which signals the P0420 code.
Common Symptoms of a P0420 Code
In most cases, the only symptom that the driver will notice is a turned-on check engine light. Rarely it is followed by performance issues and a strong smell of fuel.
Vehicle Performance Issues
Sometimes the driver will experience problems with acceleration, lack of power, and misfires. These problems mostly are the result of some other issue, like faulty spark plugs. But, there are cases when a bad CAT converter can lower the performance of the vehicle.
Unusual Exhaust Emissions
The smell of rotten eggs can come as a result of a faulty catalytic converter. That is a sign that the level of oxygen in the fuel is low. That causes excess levels of sulfur in both the fuel tank and exhaust gases, resulting in a strange smell.
Also, a driver can experience a bad surprise when his vehicle fails the emission test. The vehicle will not pass the emission test if it has any error codes that point to a problem with the catalytic converter. The test measures the level of dangerous emissions. If the CAT converter is not working properly, the emission level will be too high.
Check Engine Light Activation
The first, and usually, the only symptom that comes with this trouble code is the check engine light. As soon as the engine control unit gets the information about bad readouts on the O2 sensors, it will put out an error code and activate the check engine light. For most drivers, that is enough to check their vehicle and resolve this issue.
Check Out Car Electrical Problems: What Causes This Trouble?:
What Triggers the P0420 Code?
Understanding Data from Your Oxygen Sensors
The O2 sensors play a major role in the combustion process. They measure the level of oxygen in the emission. With that information, the ECU can perfectly balance air and fuel. That is essential for the combustion and the overall work of the engine.
The perfect and only acceptable ratio between air and fuel is 14.7:1 in favor of air. So, to burn one 1kg of fuel, the engine needs 14.7 kg of air. If there is too much air in the mix, that will lead to a lean fuel mix. To avoid that problem the ECU must send information to add fuel. In some situations, that can lead to a rich fuel mix.
Potential Problems with the Catalytic Converter
A catalytic converter, like any other component, has its work life. They usually work properly between 70,000 and 100,000 miles. When they pass their work life, then they will not be able to properly burn the bad emissions.
Unresolved issues with the engine, like misfiring, will shorten its life significantly. That is why it is very important to check for additional engine codes and address any problems as soon as possible.
Factors That Can Influence the P0420 Code
There are other factors, besides a faulty catalytic converter that can cause an engine code P0420. The most common are:
- Faulty O2 sensor. If the sensor is not working properly, it will send the wrong information to the ECU.
- An exhaust leak. If there is a leak in the exhaust, that will result in a rise in bad emission.
- Damaged oxygen sensor wiring. Problems with the sensor’s wiring are common. They are exposed to debris, dirt, and high temperatures, causing them to fail.
- Bad spark plug(s). If there is a problem with the spark plugs, then the unburned fuel will end up in the catalytic converter. That will not only shorten the life of the converter but will impact the catalyst efficiency.
- Clogged air filter. If the air filter is clogged then the air cannot properly reach the engine. That can cause several problems, with the P0420 code being one of them.
- An engine oil leak in the exhaust system. Since the converter is a part of the exhaust system, an oil leak into it will cause problems for the converter.
- Using leaded gasoline. If the manufacturer recommends using unleaded gasoline, adding leaded gasoline can lead to P0420 code.
- Damaged exhaust manifold. If the exhaust manifold is damaged it can prevent exhaust gases from leaving the engine. This will take a toll on the converter’s work.
How to Diagnose the P0420 Code
Steps for Proper Diagnosis
- Use an OBD-II scanner to check for errors. If there are other errors you should address them first
- Delete the errors and do a test drive. To be sure will the P0420 error return and when, do a 15-minute test drive. Use the OBD-II scanner to determine when and in what conditions the error will come up
- Check the exhaust system for damage. That includes the exhaust pipe, the CAT converter, the muffler, and the exhaust manifold. They can be dented, cracked, or rusted, resulting in exhaust leakage
- Test the oxygen sensor. For this, you will need a multimeter. Let the system cool down before starting the test. Adjust the multimeter to DC voltage mode. Put the multimeter clamp on one of the sensor heater power wires. Turn the engine on, and watch the readouts. The multimeter should show between 0.25A and 1.5A depending on the type of the sensor.
Check Out the How To Diagnose A P0420 Catalytic Converter Low-Efficiency Code Plus Exhaust Leak Testing:
Necessary Tools and Equipment
For diagnosing the P0420 code you will need some basic tools like a ratchet a flat screwdriver, and a multimeter.
Importance of a Thorough Investigation
Diagnosing the underlying issue of a P0420 code is not an easy task. Drivers often replace the O2 sensor, thinking that it is a simple and sure solution. But, the O2 sensor is not always the issue, and that is why the real problem must be found.
If the driver cannot go through the whole diagnostic process, then he should hire an expert mechanic to resolve CAT converter issues. If not, the car can still run with a serious engine problem, which can end up with dangerous internal engine damage.
Effective Solutions for a P0420 Code
Do-It-Yourself Fixes for the P0420 Code
Some simpler repairs can be done at home. Those include cleaning the catalyst converter, replacing the oxygen sensor and its wiring, or fixing smaller exhaust leaks. The least that you can do is to check the car for error codes.
If the scanner shows error codes between P0301 and P0308 then the engine is misfiring. The common reason for that state is faulty spark plugs.
If you detect error codes P0171, P0172, P0174, or P0175, then the engine is running in lean or rich. That means that there is too much air or fuel in the combustion process. The underlying issue for this problem can be a faulty fuel injector, high or low fuel pressure, or almost any faulty engine sensor.
When to Seek Professional Help
If you cannot diagnose the issue that is causing the P0420 don’t wait to contact the repair shop. A wide array of problems can cause this issue, and not everyone can get to the bottom of it. In case you have performance issues like a misfiring engine, act fast. They can damage your engine and cause catalytic converter failure very fast.
Potential Costs Involved in Repairing a P0420 Code
- Oxygen sensor replacement can cost between $20 and $500, depending on the exact vehicle in question
- An OEM catalytic converter can cost between $200 and $3,500, depending on the model of the vehicle. Universal-fit converters are easier to find and are cheaper
- Fixing an exhaust leak can cost between $100 and $400, depending on the damage to the exhaust.
FAQs about the P0420 Code
Is a P0420 Code Always Associated with a Catalytic Converter?
No, a P0420 code is not always associated with a catalytic converter. While a damaged or worn converter is the most common cause of the P0420 code, other issues can cause it. The usual culprits are a faulty oxygen sensor and its wiring, a leak in the exhaust, and problems with the exhaust manifold.
How Can I Turn Off the Check Engine Light P0420 that Appeared After I Changed My Oxygen Sensor?
If you changed the oxygen sensor, and the check engine light is still on, then something else is the issue. That is why you should not start replacing parts before you diagnose the problem. Yes, the catalytic converter and the oxygen sensor are the most common culprits of the P0420 error code, but there are other reasons for it. First, diagnosis, then fixing the problem.
If you diagnosed the P0420 and you sure know that the problem is in the oxygen sensor, then replace it. If the check engine light is still on, use an OBD-II scanner to erase all the error messages. If you fixed the issue, then the check engine light and the P0420 error should not return.
What Does a P0420 Error Code Signify After Changing the Air Filter?
If the P0420 error code is still there after replacing the air filter, that means, that the real issue is somewhere else. Check the catalytic converter, the oxygen sensors, and the exhaust system.
Why Am I Still Receiving a P0420 Error Message After Replacing My Catalytic Converter?
The reason for the P0420 error message is not always a catalytic converter failure. That is why it is necessary to diagnose the problem and avoid wasting money on parts that are working fine.
How Long Can You Drive with the P0420 Error Code?
There is no certain safe period that you can drive with a P0420 error code. That depends on the problem that is causing the P0420 code. If there are no performance issues, then it is okay to drive for a short period, but still resolve the issue as soon as possible. If there are other issues with the engine, then you should refrain from driving, and visit a mechanic.
Need More Help with a P0420 Code?
A P0420 code is a tricky code. In some cases, it points to a minor issue, but it can also put the engine in danger. Also, it can be very difficult to find the right cause for this code. So if you cannot find the underlying issue, do not try to resolve the problem by buying a new converter. Save money, and hire a professional to find out what is the real problem.
