An engine management code or check engine light may be caused by a variety of problems, many of which don’t actually cause your vehicle to break down or run poorly. The P0420 code signals a low catalyst system efficiency. This code suggests that the oxygen levels are below the desired threshold (Bank 1), which most often results from problems with your car’s exhaust or fuel systems. It can sometimes be tricky to diagnose, but here are five common reasons why this is occurring and how you can resolve it so your vehicle runs like new again!

A Faulty Oxygen Sensor

The oxygen sensor's job is to regulate how much air (from the outside of the car) enters your exhaust system. They check your engine's air-to-fuel ratio and adjust it accordingly. If there's not enough oxygen in the fuel, the sensor can send a signal to your car that tells it to compensate for the lack of oxygen by increasing fuel delivery. Too much oxygen or a break in the wiring can also cause this condition.

Fix p0420

What do I do if my mechanic says I need a new catalytic converter? Converters usually last between 60,000 and 100,000 miles. However, their age may depend on their design. An OEM converter will likely last longer than an aftermarket one. You may have to have a custom converter made from parts sourced from another vehicle in order to fix p0420 code problems - sometimes at an extra cost of up to $1,500+. Replacing the Converter: A broken catalytic converter needs to be replaced as soon as possible because it cannot effectively get rid of all emissions coming out of your tailpipe - which causes health risks and higher pollution levels!

An Engine That's Running Lean

A check engine light with a P0420 code means you may have an issue with your car's exhaust or fuel system. The fix p0420 could be as simple as replacing a part of your car, but it can also signify that something major like a failed catalytic converter needs to be replaced. Other reasons for a low catalyst system efficiency include: sensor issues, misfiring cylinders, problems with the oxygen sensor in Bank 1, and deteriorated vacuum hose. For more information about how to fix p0420 specifically or how to find what is causing low catalyst system efficiency in general, contact your trusted mechanic for help. 

If you don't want to wait around for hours at a service station, paying $150+ per hour for them to diagnose your car, there are things you can do yourself. It will take some time (usually 2–3 hours) and effort on your part, but fixing p0420 isn't rocket science either. If possible, try getting familiar with common repair procedures beforehand by watching YouTube videos or visiting online forums where other mechanics regularly post their questions and answers on solving fix p0420 issues (make sure they're not copy/pasted from somewhere else!). You should also call ahead to make sure they stock what you need before leaving home. Driving over during business hours (unless it's an emergency) is preferred since shops get very busy during peak periods such as holidays.

An Exhaust Leak

If you're experiencing a P0420 and your exhaust smells like it's leaking, the problem may be in the manifold or catalytic converter. If the leak is coming from the exhaust manifold, take your car to an auto-repair shop for a new gasket. A catalytic converter might have failed due to corrosion or clogged fuel injectors. You can also try removing any obstruction that may have caused a backpressure leak. 

If you're still experiencing trouble after inspecting your exhaust system, then it's time to get some help from a professional mechanic who can pinpoint the problem and fix p0420! 

A variety of catalytic converter replacement parts exist, but if they don't resolve your problem then an underlying issue probably exists. Before replacing anything else, your car may need another tune-up or even diagnostics to determine what’s going wrong. Getting diagnosed by an auto repair pro would be ideal at that point.

Fix P0420 - Third Paragraph: A clean air filter might also play a role in why p0420 keeps popping up on your dashboard screen; according to research , dirty filters cause cars to use more fuel by as much as eight percent.

Contaminated Fuel

Before you drive to the gas station, you might want to check your fuel filter first. A malfunctioning fuel filter can allow contaminants and sediment into the engine, which will lower your catalyst efficiency below threshold. Another likely cause of a low catalyst efficiency is a clogged oxygen sensor that may be incorrectly reading the exhaust fumes as normal levels of oxygen. If this is happening, then it's time for an oxygen sensor replacement. A clogged catalytic converter will also lower your catalyst system efficiency below threshold, so it's important to look at both the exhaust and intake air flow when diagnosing a faulty converter.

Failing spark plugs will result in lower catalyst efficiencies too.

Incorrect Spark Plugs

For many reasons, your spark plugs could be the cause of your catalyst system efficiency below threshold. The first reason that you may have low catalyst system efficiency and need to replace the spark plugs, is if your engine has a buildup of carbon from not using the correct type of oil. If this buildup builds up enough then it can cause an excessive amount of fuel in the exhausts to return back into the intake and contaminate your engine. Another potential scenario for catalyst system efficiency problems could stem from faulty connections. Faulty connections between the two cylinders on a two-stroke engine will eventually build up some corrosion in them and it will shorten their lifespan considerably. Leaky valves are also another factor that could reduce catalyst system efficiency because valves close prematurely due to excess pressure.