The P0420 code is a typical emissions diagnostic trouble code (DTC) many drivers encounter. Like other DTCs, this error code indicates an issue that requires immediate attention. You may notice several performance issues when driving, signifying problems in the emissions control system or engine.
But will P0420 code clear itself? The truth is that some situational error codes will clear themselves after driving for a while. However, permanent DTCs require fixing the underlying problem first to clear them.
I will help you know if the P0420 code can clear itself and what to do if it fails. I’ll also discuss the causes of this code and effective fixes.
Question: What Does the P0420 Code Mean?
The P0420 DTC stands for “Catalyst System Efficiency Below Threshold (Bank 1).” In other words, this code means you have a bad catalytic converter failing to reduce pollutants.
When your car’s PCM detects a problematic catalytic converter, it will store this code. A check engine light will accompany this code to notify you of an imminent issue.
The catalytic converter is part of the emission system that prevents pollutants from escaping. It converts/breaks down harmful pollutants from the combustion chamber into less toxic compounds. The converter will reduce over 90% of harmful substances in the exhaust system.
But how does the PCM detect issues with the catalytic converter?
Two O2 sensors – one in front and another behind the converter – monitor the converter’s efficiency. If its efficiency is low, these sensors will notify the PCM, leading to the P0420 code.
Defective O2 sensors, among many other issues, can also trigger this code. These issues will cause the converter to malfunction, resulting in a failed emissions test. Ignoring this code might lead to engine overheating, poor performance, and damage to engine parts.
Question: Will P0420 Code Clear Itself?
Several issues in the engine, fuel system, and emissions system can trigger the P0420 code. If the problem is intermittent, this code will clear itself after driving a few miles.
For instance, engine misfires will cause the converter to malfunction. However, some misfires can dissipate after several driving cycles or after accelerating. In this case, the converter will regain its normal operations, and the code will clear itself.
But in most cases, the P0420 code remains until you’ve addressed the underlying problem(s). Some drivers will use their diagnostic tools to delete this code. However, deleting a DTC with a scanner doesn’t resolve the underlying problem. The code will reappear after driving for a while.
The best way to deal with this code is to identify and fix the root cause.
Answer: How to Diagnose P0420 Code
You can diagnose the P0420 code in the following ways:
- Connect your OBD-II scanner and check for related DTCs. Pay attention to trouble codes related to the engine, fuel, and exhaust system.
- Heat your engine and use a laser thermometer to check the catalytic converter’s temperature. A difference in temperature between the converter’s front and rear means it’s functional.
- Access the catalytic converter’s pipe and remove it. This will help you examine the converter for clogs or damage.
- Use your digital multimeter to test the O2 sensors.
Question: What Causes P0420 Code?
Usually, a malfunctioning catalytic converter and a bad O2 sensor are the leading causes of code P0420. Before you check the converter, examine the two O2 sensors to see if they function correctly. You can use a multimeter to check the sensor’s ohms.
Clean your sensors with a carburetor cleaner, gasoline, or WD-40 if they appear dirty or corroded. However, if the multimeter proves the sensors are defective, replace them. Installing new sensors should allow the converter to function. If that fix fails, check the converter for defects.
You may start by cleaning your catalytic converter with soapy water or pure vinegar. A wire brush can also help remove carbon buildup in the converter and exhaust pipe. If your converter won’t work after unclogging it, replace it.
If you’ve fixed the sensors and converter, but the code won’t go, there are other issues you need to address. Below are other causes of the P0420 code:
Engine Misfires
Engine misfires are among the leading causes of malfunctioning catalytic converters. Misfires will damage your vehicle’s converter, reducing its useful life by years. Sometimes, these misfires can melt the converters, leading to premature failure.
Start by inspecting the spark plugs. Loose, dirty, or fouled spark plugs will cause misfires in the cylinders. Clean the plug and secure their connections. If you encounter fouled spark plugs, replace them.
Engine Runs Rich
Engine running too rich can cause damage to the catalytic converter. A rich mixture will cause unburned fuel to enter the exhaust and overheat the converter. So, start by identifying the cause of your engine running rich.
Clean a dirty MAF sensor or replace it if it is faulty. Other components you’ll need to check include:
- The fuel pressure regulator
- Intake temperature sensor
- Fuel injectors
- Engine coolant temperature sensor
Replace these components if necessary.
Exhaust Leak
A leak in the exhaust can draw more oxygen into the exhaust, destabilizing the O2 sensors. This issue will create a lean condition in the combustion chamber. As a result, more fuel will be added to the mixture and cause excess mixture to go into the exhaust.
The unburnt fuel mixture will overheat the catalytic converter and clog the system. If you detect an exhaust leak, take your car to an expert to patch the damaged area. Your mechanic may also replace the damaged parts.
Fixing the above issues should help clear the P0420 code. Sometimes, you’ll need to drive a few miles to clear this code and the check engine light. You can also clear the codes with your scanner to turn off the check engine light.
If none of these fixes work, seek professional assistance.
Answer: Common Symptoms of P0420 Code
We’ve addressed one of the most common emissions queries: will P0420 code clear itself? Since this code might not clear itself, it’s essential to know the accompanying symptoms.
The following symptoms might accompany the P0420 code:
- A check engine light on the dash
- Decreased fuel efficiency
- Your vehicle not exceeding 30-40 mph
- Loss of power
- Rotten egg smell
- Engine burning oil
- Hard shifting
- Rough idles
- Smoke from the tailpipe
- Air-fuel mixture imbalance
Question: Can You Drive With a P0420 Code?
Yes, you can continue driving with the P0420 code. If the code and the warning light appear suddenly, you can drive to the nearest repair shop to fix the problem. Avoid driving at high speeds to minimize damage to various engine parts.
Driving with this code will do more harm than good. The code means you have a problematic catalytic converter, O2 sensors, fuel system, and engine parts. Continuous driving can wreak havoc on your engine, fuel system, and exhaust parts. Get this code fixed ASAP to prevent further damage.
Final Thoughts
The P0420 code can signify several issues with the catalytic converter, O2 sensors, engine, and fuel system. But will P0420 code clear itself? Unfortunately, this code doesn’t always clear itself. You must identify and address the underlying problems.
I’ve shown you how to diagnose the code and how to fix the common causes of P0420 code. If dealing with this code seems intimidating, seek professional help from a certified mechanic.