What is the code P0420 on a Chevy Cruze?

The Chevy Cruze P0420 code is a diagnostic trouble code that indicates an issue with the vehicle's catalytic converter. This code is triggered when the engine control module (ECM) detects that the catalytic converter is not functioning efficiently, which can lead to increased emissions and decreased fuel economy.

What is the Chevy Cruze P0420 Code?

The P0420 code on a Chevy Cruze is a generic diagnostic trouble code that indicates a problem with the vehicle's catalytic converter. Specifically, the code is triggered when the ECM detects that the catalytic converter is not efficiently converting the exhaust gases into less harmful substances. This can be caused by a variety of factors, including a faulty catalytic converter, a problem with the oxygen sensors, or issues with the engine's fuel system.

Causes of the P0420 Code

• Faulty Catalytic Converter: The most common cause of the P0420 code is a problem with the catalytic converter itself. Over time, the catalytic converter can become clogged, damaged, or simply wear out, reducing its efficiency.


• Oxygen Sensor Issues: The oxygen sensors in the vehicle's exhaust system provide feedback to the ECM about the air-fuel ratio. If these sensors are not functioning correctly, it can trigger the P0420 code.


• Fuel System Problems: Issues with the fuel system, such as a faulty fuel injector or a problem with the fuel pressure, can also cause the catalytic converter to become less efficient, leading to the P0420 code.


• Engine Misfiring: If the engine is misfiring, it can cause unburned fuel to enter the catalytic converter, which can damage or degrade the converter over time.

Diagnosing and addressing the underlying cause of the P0420 code is important to ensure the proper functioning of the catalytic converter and to maintain the vehicle's emissions and fuel efficiency.

Symptoms of the P0420 Code

The most common symptoms associated with the P0420 code on a Chevy Cruze include:

• Decreased Fuel Economy: As the catalytic converter becomes less efficient, the vehicle's fuel economy may decrease.


• Increased Emissions: The catalytic converter is responsible for reducing the vehicle's emissions, so a problem with the converter can lead to increased emissions.


• Check Engine Light: The P0420 code will trigger the check engine light on the vehicle's dashboard.


• Rough Idling or Stalling: In some cases, a problem with the catalytic converter can cause the engine to idle roughly or even stall.

If you notice any of these symptoms in your Chevy Cruze, it's important to have the vehicle diagnosed and the P0420 code addressed as soon as possible to avoid further damage and ensure the vehicle's proper operation.

What causes P0420 in Chevy Cruze?

The conversation revolves around a Chevrolet Cruze owner experiencing a P0420 code issue, which is related to the catalytic converter. The owner and other members discuss possible solutions, including replacing the oxygen sensor, catalytic converter, or using a spacer to clear the code.

How do you know if your catalytic converter is bad on a Chevy Cruze?

There are other symptoms of a bad catalytic converter including, sulfur/rotten egg like smell, dark exhaust smoke, and high amounts of heat from beneath the vehicle. If you notice any of these signs, it is important that you get your catalytic converter checked by a technician.

How to resolve code P0420?

To fix a P0420 code, first check for exhaust leaks and test the oxygen sensors, as these are the most common causes. If the code persists, the catalytic converter is likely faulty and will need replacement, though sometimes a clogged or failing converter can be addressed with a cleaning product or by addressing engine misfires that may have caused it to fail. 
Step 1: Check for and repair exhaust leaks 

• Inspect the entire exhaust system, from the engine to the tailpipe, for any cracks or holes. 
• The oxygen sensor readings can be skewed by air entering the exhaust system from a leak, causing a false P0420 code. 
• Seal minor leaks or replace damaged sections of the exhaust pipe. 

This video demonstrates how to inspect the exhaust system for leaks: 53sFlat Rate MechanicYouTube · Dec 8, 2022
Step 2: Test the oxygen sensors 

• A faulty oxygen sensor is a very common cause of the P0420 code. 
• Use a scan tool with live data to check the readings from both the upstream and downstream oxygen sensors. 
• The downstream sensor's readings should be stable and consistent, while the upstream sensor's readings should fluctuate. 
• If the downstream sensor's readings are fluctuating similarly to the upstream sensor, it may indicate a failed catalytic converter, or a bad oxygen sensor itself. 
• If the downstream sensor is faulty, replace it. 

Step 3: Address other potential engine issues 

• Perform a tune-up by checking and replacing any worn spark plugs. 
• Check for other engine codes and address issues like misfires or rich/lean conditions, which can damage the catalytic converter. 

Step 4: Replace the catalytic converter 

• If the above steps do not resolve the issue, the catalytic converter is likely the problem. 
• Before replacing it, ensure that there are no other issues like misfires, as this can damage the new converter. 
• This is often the most expensive fix, so it should be done only after confirming it is necessary. 

Step 5: Reset the code and monitor 

• After performing any repairs, reset the check engine light using a scan tool. 
• Drive the vehicle to see if the code returns. If it does, the problem is not fixed. If it doesn't, the issue may be resolved. 

What is the most common cause for a P0420 code?

The most common causes of a P0420 code are a faulty catalytic converter and a bad oxygen (O2) sensor. Other frequent culprits include exhaust leaks, engine misfires, and sometimes an issue with other components in the exhaust or fuel system. 
Common causes of P0420

• Catalytic converter failure: This is often the primary cause, as the converter's ability to convert emissions is reduced over time. 
• Faulty oxygen sensors: The oxygen sensors are critical for monitoring the catalytic converter's efficiency. If one is sending incorrect data, it can trigger the P0420 code even if the converter is fine. 
• Exhaust leaks: An exhaust leak can allow outside air into the exhaust system, which throws off the oxygen sensor readings and makes the system appear inefficient. 
• Engine misfires: If the engine is misfiring, unburned fuel can enter the exhaust system. This can overheat and damage the catalytic converter over time. 
• Other issues: Problems with spark plugs, fuel injectors, or even certain fuel additives can also contribute to a P0420 code. 

Diagnosis and next steps

• Check oxygen sensors: A mechanic can use a professional scan tool to check the live data from the oxygen sensors. If the readings from the upstream and downstream sensors are too similar, the converter is likely failing. 
• Inspect for leaks: A visual inspection can reveal leaks, and a shop can use a shop vacuum and soapy water to help find them. 
• Address other engine problems: Before replacing the catalytic converter, it is crucial to ensure there are no other engine issues, like misfires or fuel delivery problems, that could have caused the converter to fail.