The P0420 code signifies a problem with the catalytic converter or more serious repairs. If the code shows in the car’s PCM, then it means it has identified a problem; in this case, with the catalytic converter.
The catalytic converter reduces emissions that exit the car through its exhaust pipe and removes harmful pollutants that were created during combustion in the engine.
The driver is not under any risk of harm related to the P0420 code, but they should have the problem fixed sooner rather than later to avoid further issues, as failing an emissions test.
Our opinion is that you shouldn’t drive your car until you have fixed the P0420 code. There are some repairs related to the P0420 code that you can do yourself, but many of the more extensive repairs will need to be handled by a mechanic.
What is the P0420 code?
Code P0420 indicates low efficiency in the catalyst system. P0420 indicates that the oxygen levels in your car (Bank 1) are lower than the expected level. Most commonly, this is due to the fuel or exhaust systems.
This can be challenging to diagnose sometimes. Put simply, P0420 means that the catalytic converter is not functioning effectively in removing pollutants from the exhaust. The emissions test on your vehicle will fail.
A bad catalytic converter does not pose a danger to the driver, but it can overheat and potentially cause damage to the internal components of the engine.
In general, the P0420 engine problem does not pose a safety risk to driving. It is probably not an issue that would affect reliability or drivability. However, because the catalyst system on bank 1 is failing, it may be releasing more harmful pollutants.
Therefore, your chances of passing emissions tests are slim if the check engine light is on, just with the P0420 code.
As with any engine problem, the best option is to repair the P0420 issue as quickly as possible. Therefore, we do not recommend you wait weeks or months to address these issues.
That being said, it is probably safe to drive with the P0420 engine code. Just be conscientious, there are other engine codes, obvious symptoms, etc., if driving the vehicle feels dangerous, please act accordingly.
Summary of p0420 error code:
- P0420 meaning: Catalyst system efficiency below threshold (Bank 1)
- How serious is it: MODERATE – Driving with this code carries potential internal engine damage while driving over a long period if the fault is not promptly addressed.
- Repair urgency: Get this code fixed as quickly as you can to prevent potentially greater damage to your engine and possible engine damage.
- Diagnosis: The usual cause of P0420 is a damaged catalytic converter; however, it could also be due to misfires, a defective oxygen sensor, excess or deficient air/fuel mixture, potentially a range of bad oxygen sensors, or other potential causes.
Can I drive with the P0420 code?
In the short term, it is usually acceptable to drive with a P0420 code. The driver is at no risk due to this code. This code can cause harm to your engine and exhaust system if you drive it for an extended period.
If you notice this code, you do not need to get a tow truck, at least not yet; however, if this code comes up, you should do your best to rectify the problem as soon as practical. You could have more noticeable issues with how your car performs.
This is due to your exhaust system not performing correctly. It could be more problematic if the other codes indicate too much fuel in your air/fuel mixture.
Look for any other codes, particularly P0171, P0172, P0174, or P0175. These codes could indicate that your engine has the wrong balance in fuel-to-air ratio.
What causes the P0420 error code?
The faulty catalytic converter is the most common reason behind the P0420 error code.
Other less common reasons may include:
- A bad exhaust pipe or leaking exhaust pipe.
- An engine misfire.
- A bad exhaust manifold or an exhaust manifold leak.
- Not connecting the oxygen sensor wiring.
- Bad oxygen sensor pigtails.
- A bad muffler or a muffler that leaks.
- A bad rear oxygen sensor.
- Oil contamination of the catalytic converter.
- A bad front oxygen sensor.
- Bad oxygen sensor wiring.
- A bad engine coolant temperature sensor.
How do I diagnose P0420?
Four important steps must take place in the diagnosis of P0420:
1. Confirm there are no other codes
You should deal with any other codes first, since these codes could be the cause of the P0420 error. An OBD2 scanner can reveal if there are any other codes. If there are any codes like P0300, P0171, etc, they could be the source.
Only after correcting these codes can you replace your catalytic converter. If you replace the catalytic converter before correcting the other code, your new catalytic converter will fail again.
2. Clear the code and drive to see if it returns
You can also check to see if the code is random by clearing the code and driving.
Sometimes a sensor in your car sees abnormal patterns. Once that abnormal pattern has been seen over a long period of time, there is either a problem with the sensor or a problem with the vehicle. The check engine light turns on as a result.
So, even if the condition may resolve itself after a few periods, you should try to see if your check engine light turns on. Go ahead and turn off your check engine light. Then keep driving for about 15 minutes to see if the check engine light comes back on.
If it doesn’t come back on, then it probably was a temporary error, and you can leave it alone. But be careful. If the check engine light comes back on quickly after you turned it off and throws the same code, it is probably a problem you need to figure out and repair.
3. Check for leaks in your exhaust system
If, after clearing the code and driving, you’ve confirmed the P0420 is still there, you should do a check of the exhaust system. You should inspect the exhaust system, particularly what is done before the catalytic converter. Check for leaks, rust, holes, etc.
Check the gaskets, exhaust pipes, and exhaust manifolds. You have to fix any leaks or damage you find.
4. If you have to replace the catalytic converter, check the downstream O2 sensor
Start your vehicle and make sure the engine is at normal operating conditions. Then use a digital multimeter to check the voltage of the downstream O2 sensor.
The downstream O2 sensor should be approximately 0.45 volts, indicating the catalytic converter is working properly. If the voltage fluctuates between 0.1 and 0.9 volts, then the catalytic converter must be replaced. This final voltage indicates that the catalyst section in the Catalytic Converter is not working properly.
What Are The Symptoms Of The P0420 Code?
The only P0420 code symptom that is brief or typical is the check engine light illuminating.
Secondly, you may have trouble achieving a speed greater than 30 to 40 mph because your engine will not perform as smoothly as it normally does. The engine will then provide low power make it impossible to accelerate.
How Much Does It Cost To Have A Professional Fix The P0420 Code?
The cost of having a professional repair the P0420 error code in your vehicle can vary widely based on several reasons including vehicle make and model, severity of issue, and location of the shop.
P0420 code repairs can typically cost anywhere from $100 to $1,000 or even higher, depending on the exact problem causing the code, the parts needed for the repair, and the labor costs at the repair shop.
The P0420 code is commonly associated with catalytic converter issues, which can be very costly to replace. Other times the issue could be an O2 sensor or some other cheaper parts.
It is wise to obtain a written estimate from an honest mechanic before proceeding with repairs, so you are fully informed of the costs involved.
FAQs.
Which O2 sensor causes P0420?
When the oxygen sensors upstream and downstream detect that the catalytic converter is not functioning properly, a P0420 code is triggered. In essence, the downstream sensor recognizes that some of the oxygen entering the converter is not being burned.
Will a P0420 code cause a misfire?
In a nutshell, P0420 can and will make a car lose its ability to accelerate and/or experience multiple misfires or selective cylinder misfires. Your congested exhaust is most likely the source of your issue, which will result in excessive backpressure and a loss of power.
Where is P0420 Bank 1?
When your car’s computer receives the P0420 code, it means the Bank 1 catalytic converter isn’t performing as it should. The side of the engine that contains the first cylinder is referred to as “Bank 1.” Bank 2 is located on the engine’s opposing side.
Why am I still getting a P0420 code after I replaced my catalytic converter?
O2 sensors before and after the catalyst as well as the catalyst itself may be to blame for the code P0420. You might have an exhaust leak at the manifold or pipes if both the O2 sensors and the catalyst were replaced.
How long does it take for P0420 to clear?
Reset the code and continue driving for around 15 minutes. Check if the code is returned. If not, try it again a few times to be certain. When the DTC P0420 appears, a real issue exists.