Table of Contents
The catalytic converter is considered one of the most important parts of the vehicle. It helps to lower the emissions of exhaust gases. The main purpose of the catalytic converter is to convert the dangerous pollutants produced during the combustion cycle into less hazardous emissions. The P0420 code indicates an issue with the catalytic converter.
The catalytic converter is a costly part. The powertrain control module (PCM) constantly monitors the performance of the catalytic converter. When it observes an issue with Bank 1 catalytic converter, it triggers the engine code P0420. This article explains the P0420 code meaning, causes, symptoms, and how to fix it.
P0420 Code Definition
The P0420 code stands for “Catalyst System Efficiency Below Threshold (Bank 1).”
What does the P0420 Code Mean?
The P0420 code indicates that your vehicle’s powertrain control module (PCM) monitors the poor efficiency of the catalytic converter at Bank 1. This code may also be triggered due to a bad catalyst or a false alarm caused by a faulty oxygen sensor at Bank 1.
Basically, Bank 1 and Bank 2 are the two sides of the engine. Bank 1 represents the side of the car’s engine containing cylinder No. 1, while Bank 2 represents the opposite side of Bank 1.
The powertrain control module (PCM) of your vehicle gets information from different engine sensors. It uses this information to control engine functionality.
Each engine bank usually contains two oxygen sensors. They are both placed near the catalytic converter; one is in front of the converter (known as an upstream sensor), and the other is behind it (known as a downstream sensor). These sensors are used to measure the efficiency of the catalytic converter.
Readings of the upstream O2 sensor should vary while the engine is working at the optimal temperature or in the closed loop. This variation shows that the upstream O2 sensor is operating efficiently.
In the case of the downstream O2 sensor, its reading shouldn’t be changed if your catalytic converter is working efficiently.
There may be a problem with the catalytic converter if the readings of both O2 sensors are the same. The reduction and fluctuation in the voltage readings (like the reading of the upstream O2 sensor) of the downstream O2 sensor occur due to the high O2 level within the system. Due to this high oxygen level, the PCM will trigger the P0420, and your check engine light will start to illuminate on your car dashboard.
The efficiency of the catalyst can be reduced permanently or temporarily due to the improper fuel-air mixture, and this can be the reason for P0420.
Symptoms of P0420 Code
A car with the P0420 error code can experience one or more of the following symptoms:
1) Check Engine Light
The illumination of the check engine light is one of the most common symptoms of the P0420 trouble code. As we discussed above, the performance of the catalytic converter is monitored by the vehicle’s main computer (i.e., ECM or PCM).
Whenever the PCM notices an issue with the catalytic converter, it triggers the check engine light to alert the driver about issues. However, it may also trigger the check engine light due to many other issues. Therefore, it is recommended to properly inspect the system to find the main issue.
2) Reduced Engine Power
The reduction in engine power is one of the clear symptoms of a bad catalytic converter. When the catalytic converter goes bad, it may lead to inconsistent fuel pressure. This inconsistent fuel pressure leads to poor combustion of air-fuel mixture, causing reduced engine performance. You might also observe erratic motion while driving or instances where the engine completely stalls.
3) Inabilityto Speed Up
When the catalytic converter goes bad, it may lead to an accumulation of exhaust gases in the exhaust pipe. This buildup of exhaust gases may lead to decreased performance. As a result, your vehicle will not be able to accelerate beyond 30-40 miles per hour.
4) Fuel Smell
The exhaust system of your vehicle contains different costly parts that play a vital role to minimize exhaust noise and exhaust emissions. These components are the catalytic converter, tailpipe, car muffler, resonator, and exhaust manifold. These components operate in such a way that they stop the hazardous engine emissions from entering the vehicle’s interior.
Additionally, the exhaust system also plays a vital role in reducing emissions and protecting the environment.
When a faulty catalytic converter leads to the P0420 engine code, it can lead to an unpleasant odor resembling rotten eggs in the exhaust fumes. This smell usually occurs due to a reduction in the oxygen levels within the converter, which can lead to an excess of sulfur in both the fuel tank and the exhaust emissions.
5) Rough Idle
A bad catalytic converter may also lead to a rough idle. The rough idle usually produces due to an unbalanced air-fuel mixture.
6) Poor Fuel Efficiency
A catalytic converter may also lead to poor fuel efficiency. When it goes bad, it doesn’t efficiently convert and process exhaust gases. In such a condition, your engine needs to work harder and it consumes more fuel than usual.
7) Failed Emission Tests
As we discussed above, the main purpose of the catalytic converter is to lower the emissions of the exhaust gases. When it goes bad, it doesn’t efficiently control exhaust emissions and leads to an increase in the exhaust emissions. In such a case, your vehicle will be unable to pass the emission test.
8) Rattling Noise
A faulty catalytic converter may also lead to a rattling or rumbling noise. This noise usually produces due to loose or damaged parts of the catalytic converter.
Read Also: Causes of Check Engine Light Illumination
Causes of the P0420 Code
A bad catalytic converter is one of the major causes of the P0420. Additionally, damaged oxygen sensors, intake leaks, faulty muffler deletions, exhaust system leaks, or improper placement of the catalytic converter may also cause DTC P0420.
The primary causes of the P0420 code are listed below:
- A faulty downstream or upstream oxygen sensor
- Leakage in the exhaust system
- Damaged engine coolant temperature sensor
- Usage of the wrong type of fuel
- Damaged exhaust pipe
- Loose or improper wiring of the oxygen sensor
- The rich or lean air-to-fuel ratio
- Damaged wires or loose connections
- Damaged powertrain control module (PCM)
- A leaky fuel injector
- Engine Misfiring, which can damage the catalytic converter
- Bad catalytic converter
- Higher fuel pressure than usual
- Oil leakage in the catalytic converter
Read More: P0455 Symptoms and Causes
How to diagnose the P0420 Code?
Follow the below-given steps to diagnose the P0420 code:
- Read the trouble codes with the help of an OBD2 scanner. Write the P0420 code and all other codes stored in the PCM memory. Clear the codes and perform a test drive. If the P0420 appears again, move forward for deep inspection.
- Check the live data of the downstream O2 sensor using a multimeter. The reading of this sensor must be constant. Analyze the readings to check whether the rear O2 sensor is working efficiently or not.
- Test the upstream O2 sensor using a multimeter.
- After testing the O2 sensor, clear the codes and perform a test drive. If the code returns, perform further inspection.
- Solve all the ignition problems, misfire issues, and fuel system faults.
- Perform a visual inspection to check for any damage and wear on the O2 sensor.
- Check the wires and connectors connected to the catalytic converter and PCM.
- Inspect the exhaust system for a leak.
- Inspect the fuel injector for a fault.
- Inspect the system thoroughly to find a possible oil in the catalytic converter.
- In the case of a faulty catalytic converter, replace the converter and update the PCM.
- Inspect your PCM and replace or reprogram it if needed.
Common P0420 Code Diagnosis Mistakes
The following list contains the most common P0420 diagnosing mistakes:
- Replacing the oxygen sensors before finishing the diagnostic procedure.
- Overlooking other stored codes saved in PCM memory and solely focusing on P0420 code.
- Installing the new parts without inspecting them.
- Not using the quality parts.
- Overlooking the exhaust leaks.
- Not following the manufacturer’s diagnostic instructions
- Not using the recommended tools to diagnose the P0420 code.
How to fix the P0420 Code?
To fix the P0420 code, you need to repair or replace one or more of the following parts:
- Replace the faulty O2 sensor
- Repair the exhaust system leaks
- Fix the misfiring issues
- Fix the issues related to lean or rich fuel mixture
- Change or repair leaky fuel injectors
- Replace the air-fuel ratio sensor
- Identify and resolve any other associated error codes
- Repair the damaged wires and connectors
- Replace or repair the broken exhaust pipes
- Replacing the coolant temperature sensor
- Replace the bad catalytic converter
- Clean the catalytic converter if it is clogged
- Update the software of PCM
How to Prevent P0420 Code from Triggering?
- Always use quality fuel
- Ensure sufficient oil in your engine
- Use the correct oil grade
- Regular maintenance of your vehicle according to the manufacturer’s instructions
- Avoid harsh driving
- Address illuminated check engine light promptly
- Monitor the performance of your oxygen sensor regularly
- Avoid idling your engine for a long time
Code P0420 Repair Cost
The repair cost of the P0420 code varies according to relevant part repair, vehicle model, and labor cost. If the P0420 code is triggered due to a faulty catalytic converter, your mechanic may cost from $480 to $1610 to fix it.
The estimated cost of repairing the P0420 code is given below. The prices include parts and labor work at a workshop.
| Parts | Cost |
|---|---|
| Catalytic Converter Replacement | 480$ to 1610$ |
| Downstream O2 Sensor Replacement | 130$ to 320$ |
| Upstream O2 Sensor Replacement | 140$ to 320$ |
| Air fuel sensor replacement | $200 to $320 |
| Exhaust leak repair | $100 to $220 |
FAQ Section
How serious is the P0420 code?
P0420 code is not so serious. In most circ*mstances, this code won’t cause any serious issues for the engine of your automobile. The worst thing that can happen in the case of P0420 is a blockage in the exhaust flow due to any broken internal part of the catalytic converter. But still, there is a very low probability of this happening.
Can a bad O2 sensor cause a P0420 code?
Yes. The normal catalyst monitor uses the downstream O2 sensor signal to calculate the efficiency of the catalyst, while the upstream O2 sensor signal is used as the reference point. Therefore, the P0420 code can be set when either the upstream or downstream O2 sensor goes bad.
How do I clear a DTC P0420?
Use a code reader or scan tool to clear the P0420 code temporarily. The main issue is that when the PCM of your runs its system self-test, it returns a code. In order to close the code and keep it closed, you must first find and resolve the underlying issues that triggered the code and then use a scan tool to clear the code.
Can I drive with a P0420 Code?
Yes, you can drive your car with code P0420, but experts don’t recommend it. Driving a vehicle with a P0420 can badly damage your vehicle’s catalytic converters. This issue may also damage other parts of your car, like the fuel lines and the exhaust system. That’s why you must regularly inspect your car’s catalytic converter to avoid further costly repairs.
What can damage the catalytic converter?
- Misfires
- Intake leaks
- Bad powertrain control module
- Oil consumption
- A lean or Rich air-fuel mixture
- Lean mixture
- Exhaust leaks
What is the P0420 code on a Chevrolet?
When your Chevrolet is experiencing a p0420 code, it is usually caused by an exhaust leak before the catalytic converter. It may also trigger due to a bad catalytic converter or downstream (back) O2 sensor. Chevrolet engines have been known to leak around the exhaust manifold. So, if you notice a strange noise when the engine is running, be sure to check it out.
Read More
- PCM Function, Symptoms, and Causes
- Bad O2 Sensor Working, Symptoms and Causes
- P0017 Code Symptoms and Causes
- P0453 Symptoms and Causes
- P0507 Symptoms and Causes
- P0452 Code Meaning and Causes
