What is P0420 DTC? Common Symptoms, Causes, and Solution
A foul fuel smell from the exhaust pipe or a drop in the acceleration performance is always a sign that your vehicle’s emission system is malfunctioning. And if the hand-code reader is showing P0420 code, it means that the catalytic converter is working below its efficiency.
The following are the key takeaways from this article:
P0420 is an intermediate DTC indicating a catalytic convertor working below its efficiency.
The common signs of this DTC are the check engine light, foul fuel smell from the muffler tip, limited acceleration, and an overheated car.
P0420 can occur due to a damaged exhaust pipe, increased fuel pressure, a malfunctioning catalytic converter, or a malfunctioning sensor.
You can reset the DTC and test drive the vehicle to check if the engine fault code occurred due to an ECU error.
Else try replacing the muffler tip, exhaust pipe, oxygen sensor, or catalytic converter, depending on the root cause of this DTC.
These solutions can be as inexpensive as $20 (in case of oxygen sensor replacement) and as expensive as $2500 (in case of catalytic convertor replacement).
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Introduction
Check engine light always warns that some engine component is malfunctioning, and the drivers should pay attention to this light. It can result in severe consequences, such as a seized engine or damage to the internal engine components (1). Suppose you see a check engine light on the vehicle’s dashboard. In that case, you should immediately connect a hand-code reader with the OBDII module to read the diagnostic trouble code.
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If the DTC is P0420, it is a sign of a fault in the catalytic converter.
Along with the check engine light, you will also face a sudden power loss, and the vehicle will drive slower (2). This article will further shed light on the symptoms, causes, and standard solutions of P0420.
Role of Catalytic Convertor in the Car
Each car on the road releases harmful pollutants, including carbon monoxide, hydrocarbons, and nitrogen oxides. With millions of cars driving around the globe, this pollution can create a significant problem and contribute to breathing illness, environmental pollution, and poor air quality. The Environmental Protection Agency (EPA) combated these harmful effects by strengthening the emission regulations. Auto manufacturers have been bound to include catalytic converters in cars in the US and Europe since 1975 (4). The catalytic converter is usually located below the car in the exhaust system. It is a structured honeycomb metal coated for ruggedness and high temperatures.
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When the exhaust gases pass through the heated catalytic convertor, the reduction catalyst reduces harmful nitrogen oxides by separating the oxygen and nitrogen molecules. As a result, the oxygen passes through the converter, and nitrogen is trapped inside the catalytic converter.
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The oxidation catalyst reduced unburned carbon monoxide and hydrocarbons by burning them over the metal catalyst. Furthermore, a well-maintained catalytic converter also improves the car’s fuel efficiency.
How to Read P0420 DTC
The following table illustrates the P0420 code interpretation (3):
Number of Character
Specific Character
What does it Signify
First
P
The problem lies within the powertrain part of the vehicle. This means that the engine, transmission, or fuel system malfunctions.
Second
0
This means that the code is standardized, so the SAE manual can be used further to interpret the code instead of the instruction manual.
Third
4
This number illustrates that the problem lies within the vehicle’s emission system.
Fourth and Fifth
20
The specific fault index is 20 indicating a low catalyst efficiency.
So, P0420 illustrates a problem in the vehicle’s emission system. Further that the DTC is SAE standardized (1). This DTC in any vehicle will indicate the same problem. Finally, the last two digits indicate a specific fault that the catalyst’s system efficiency is below the average threshold.
Symptoms of Code P0420
Rotten Fuel smell
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The major symptom of the engine code P0420 is that the exhaust of the vehicle releases gases having a rotten egg-like smell. This indicates that the catalytic converter of the engine needs to be checked.
The burning of gasoline releases harmful chemicals such as hydrogen sulfide and sulfur oxides. The catalytic converter is responsible for transforming these gases before releasing them into the air. Still, due to the poor performance of the catalytic converter, these gases are directly released into the air through the exhaust system, and a rotten egg-like smell is spread in the surroundings (1). The other reason for the bad smell from the exhaust is the defective fuel sensors. The faulty fuel pressure sensor can be the reason for destroying the catalytic converter. The defective fuel pressure sensor will block the convertor with excessive oil. As a result, sulfur will be deposited in the catalytic converter, releasing a rotten smell upon burning. Other than it, if the engine fluid is old, it will leak into the different parts and is also responsible for the poor functioning of the catalytic converter. So, suppose the rotten smell is observed. In that case, it indicates that the functioning of the catalytic converter has slowed down, and the engine light is illuminated due to code P0420 (2).
Limited Acceleration
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Due to the engine code P0420, the car’s speed would not increase by 30 to 40 mph. This usually happens because of the broken catalytic converter.
The engine’s exhaust system helps generate power (5). There is a combustion system in the engine of the vehicles that help in producing power by utilizing the air, fuel, and vacuum. The catalytic converter is responsible for maintaining the flow of air in the engine but due to the damaged and clogged catalytic convertor, the airflow in the engine is lessened, and ultimately the car fails to accelerate more than 40 mph. Thus, the reduced acceleration is the symptom of engine code P0420.
Excessive Heating
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Due to the engine code P0420, there is a possibility that the vehicle becomes excessively warm. This indicates that the catalytic converter needs to be fixed.
Thus the engine exhaust turns black. Due to the malfunctioning of the catalytic converter, a large amount of fuel is burnt. If the catalytic converter is blocked due to debris and oil, it will release a large amount of heat. As a result, the engine becomes heats up and stops functioning.
Causes of Engine Code P0420
Damaged Muffler
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The engine code P0420 might occur due to the broken muffler in the engine. Due to the broken muffler, the car exhaust will not operate properly.
It will not release the sulfides into the atmosphere. Therefore, burning fuel will release harmful gases such as carbon mono oxides and sulfides, which are deposited into the catalytic converter (3). The toxic fumes will then spread in the car’s ventilation system and is responsible for the rotten smell.
Increased Fuel Pressure
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Increased fuel pressure can be one of the major causes of the engine code P0420. This is because the engine’s high fuel pressure will increase the fuel in the engine.
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The high amount of fuel in the engine will affect its engine performance as the oil will be deposited in the catalytic converter. Also, the high pressure of the fuel will cause leakage in the engine system and is responsible for clogging different parts of the engine (1). As a result, the engine will become rough and less power will be generated. Also, the black smoke will release a bad smell from the exhaust system (4). Thus, these symptoms indicate a problem with the catalytic converter, and the engine’s working is poorly impacted due to high fuel pressure.
Damaged Sensors
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A damaged oxygen sensor can also be the reason for the engine code P0420. There are chances that the oxygen sensors are damaged or a connectivity issue between the wires and sensors.
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The sensor’s performance is almost negligible. Due to the poor performance of the oxygen sensors, the engine will consume more fuel than the requirement. This will impact the engine performance because maximum combustion will increase the oxygen-to-fuel ratio. Also, the damaged oxygen sensor will make the engine rough and noisy (2). Thus, the faulty oxygen sensor will affect the engine’s functioning, and the car’s acceleration will be slowed. Also, the poor oxygen sensors are responsible for the failure of the emission test. As a result, the engine will face trouble operating, and also the gases released from the exhaust will smell like rotten eggs. Thus, all these issues will indicate the code P0420.
Solutions to Resolve DTC P0420
Following are some solutions to resolve the P0420 DTC:
Reset the DTC and Test Drive
The most common and inexpensive DTC solution is resetting the trouble code and test-driving the vehicle. Sometimes, a DTC is displayed without an actual issue.
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In this case, resetting the DTC will resolve the issue. To reset the DTC:
Connect the hand-code reader with the OBDII module and reset the DTC (3).
Test the vehicle for a few miles to check if the warning sign appears again.
If the warning sign appears again, dig into the issue to find the root cause.
Replace the Muffler Tip/Exhaust Pipe
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There might be a chance that the DTC is displayed because of the leaks in the muffler tip. The aftermarket muffler tips are usually of low quality that can deteriorate over time.
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To resolve this issue, try replacing the muffler tip with a new one. Similarly, you can repair the leaks in the muffler tip to check if the problem has been resolved. In some cases, the exhaust pipe can also be damaged. So you can visually inspect the exhaust pipe and muffler tip for any damage (3). If the damage seems repairable, then there is no need to replace the components. Else try replacing the faulty components to resolve the DTC.
Replace the Oxygen Sensor
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Another common cause of this DTC can be a faulty oxygen sensor. The oxygen sensor may send wrong readings to the ECU, causing it to display the check engine light.
The oxygen sensor is located on the passenger side of the exhaust pipe near the catalytic converter. Try replacing the oxygen sensor to check if the DTC disappears.
Replace the Catalytic Converter
The most expensive and common solution to this DTC is the replacement of the catalytic converter.
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The catalytic converter is an expensive component; its price can vary depending on the vehicle’s make, model, and variant.
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In typical cases, the catalytic converter malfunctions due to poor vehicle maintenance. This will require you to replace the malfunctioning catalytic convertor for proper vehicle functioning (5).
Typical Cost to Resolve this Issue
The following table illustrates the typical cost required to resolve the issue:
Common Issues
The severity of the issue
Standard Cost Required to Resolve the Issue
Damaged Muffler Tip
Intermediate: The car can be driven for medium distances with this issue
$70-200 to replace the muffler tip, $40-50 to repair the muffler tip
Damaged Exhaust Pipe
Intermediate: The car can be driven for medium distances with this issue
$600-800 to replace the damaged exhaust pipe, $70-100 to repair the damaged exhaust pipe
Malfunctioning Oxygen Sensors
Low
$20-30 to replace the oxygen sensors
Malfunctioning Catalytic Converter
High: The catalytic converter should be replaced at the earliest to avoid any internal component damage
$800-2500 to replace the catalytic converter
Fuel Pump Problem
High
$500-700 to replace the fuel pump
Labor Cost
–
$20-200, depending upon the extent of the issue
Conclusion
To conclude, the P0420 is a medium emergency issue that indicates an inefficient catalytic converter. There can be different reasons for this DTC, including a damaged muffler tip, exhaust pipe, catalytic converter, or even a dirty/malfunctioning sensor. In case of a damaged muffler, or exhaust pipe, you can drive your car for intermediate distances. However, suppose the catalytic converter is malfunctioning. Then, resolving the issue immediately to prevent damage to the internal car components is recommended.
A catalytic converter is an expensive part that cannot be replaced as a part of service maintenance. Suppose you are servicing your car at regular intervals. In that case, there is a chance that the catalytic converter will work fine for even ten years. However, if the vehicle is illustrating a drop in performance or the car has failed an emission test. There is a chance that the catalytic converter is malfunctioning. So, it needs replacement.
You can slide under your car and check for visual damage on the exhaust pipe or muffler tip. Similarly, you can pull up your vehicle on a hydraulic press to conveniently check for significant damage on these parts. If the muffler tip/exhaust pipe is damaged, replacing or repairing these parts is recommended.
You can reset the DTC by connecting a hand-code reader with the OBDII module. To find the OBDII module, you can consult your vehicle’s instruction manual. Usually, the OBDII module is present below the steering module of the car.
