What Causes P0420 Code On A Car? [Solved]

While driving highway we always need power to drive-through lanes or to overtake vehicles, imagine flooring the pedal and the car isn’t giving proper response and engine light pops up and your silencer starts to spit fumes everywhere, pretty problematic right? It can be caused due to code p0420 which is a catalytic system problem, Let’s discuss what causes these problems in detail.

p0420 code means Catalyst System Efficiency Below Threshold is denoted by the code P0420. Simply put, this code means that your car’s computer has identified catalytic converter underperformance.
Several problems might cause the, Check Engine Light to light.

If you use an OBD-II scanner and obtain a P0420 code, your catalytic converter may be malfunctioning.

What Causes P0420 Code?

a catalytic converter of a modern car close up view

The P0420 error code indicates that the catalyst system is inefficient. This is frequently the result of a problem with your vehicle’s exhaust or fuel systems. It might be challenging to diagnose at times.

A catalytic converter is a component of a vehicle’s exhaust system. It works by turning unburned fuel and carbon monoxide (CO) from combustion into carbon dioxide (CO2) and water (H2O). The filters keep hazardous exhaust gases out of the environment. The catalytic converter’s function is so critical that if this component of the car fails, you will almost certainly fail an emissions test.

The front and rear, or upstream and downstream, oxygen sensors of a catalytic converter. Their task is to ensure that the catalytic converter is working correctly.

1. Causes Of The Code-

Many causes can happen on your vehicle which causes OBD reading P0420 Code, some of them are:

1. Aging catalyst that is faulty
2. A faulty oxygen sensor
3. Leaks in the exhaust, intake, or mass airflow (MAF) sensors
4. Exhaust manifold damage
5. Exhaust pipe damage

2. Symptoms Of Catalyst System Failure-

Some of the symptoms which arise due to failure of the system:

1. Inadequate throttle response
2. Higher fuel consumption
3. Rough engine operation
4. Failing the exhaust emission test
5. A strong exhaust smell emerging from the exhaust pipe

Does It Cause Damage To The Vehicle?

The flaw is unlikely to produce significant drivability or reliability problems. However, if your engine’s catalyst system is underperforming, it may be spewing more harmful pollutants. You are unlikely to pass emissions checks as a result of this, along with the check engine light.

The safest solution, like with any engine problem, is to identify and rectify the P0420 problem as soon as possible. So we’re not proposing that you ignore these challenges.
Having said that, catalytic converters are costly to replace. If the problem is not resolved quickly, it may cause serious and costly damage to other vehicle components.

Is It Safe To Drive With The Fault P0420 Code?

In most cases, it is safe to drive with P0420 present. Aside from the check engine light blinking, there may be no noticeable changes in how a car functions. If the engine is running lean, avoid driving it or, at the absolute least, keep the throttle input and RPMs low. Lean engine operation may put the engine at risk of more serious problems.

How To Fix Catalyst System Problem?

mechanic conducting diagnostics tests on a vehicle

With a scan tool or code reader, you can temporarily clear the P0420 code. The issue is that the code will reappear as soon as your vehicle’s primary computer conducts its system self-tests. To get the code to turn off and remain off, you must first resolve the underlying issue that triggered the code.

The only solution is to replace the catalytic converter. However, a catalytic converter problem might cause a slew of additional problems. You must also address those concerns before installing a new catalytic converter, or else the damage may escalate.

1. Checking O2 Sensor-

When oxygen sensors on both sides of the exhaust show similar values, the code will be thrown. When the oxygen sensor fails and presents a false value, the P0420 code is set. If the engine does not exhibit any of the reduced performance associated with a faulty catalytic converter. A faulty oxygen sensor might also be a source of concern.

We will suggest going through this tutorial before changing the O2 Sensor.

2. Checking Wirings-

The wiring for the oxygen sensor might be damaged. Because it is vulnerable owing to its constant proximity to hot exhaust. Because it is so far away from the ECM, the downstream oxygen sensor wire is also volatile. As a result, faulty O2 sensor wiring might result in code P0420.

We will suggest going through this tutorial before changing the wiring.

3. Replacing Muffler and Catalytic Converter-

Unless the engine is operating poorly when this code appears, the problem is usually connected to emissions. Aside from checking that the oxygen sensors are functioning properly, no more diagnostic is required.

Catalytic converter replacement is frequently costly. In certain situations, this repair might cost thousands of dollars, and the sort of automobile you drive will undoubtedly influence the cost.

It is a bit of a process to work on we, suggest watching this video before proceeding.

Cost Of Replacing Muffler/Catalytic System

A catalytic converter repair might cost between $1,000 and $2,500 on average. A new catalytic converter costs roughly $2,000, while an O2 sensor costs between $150 and $500.

Aftermarket or non-factory converters are sometimes available and can save you money. These non-factory converters perform almost as well as the original factory converter and can reduce the job cost to $500–$800. Aftermarket converters often do not contain the same amount of precious metal as OEM parts, so they are less efficient – but they will keep the check engine light off.


Engine Code P0420 does not commonly endanger one’s driving safety. The flaw is unlikely to create significant drivability difficulties. However, because the catalyst system on bank 1 is underperforming, your engine may be producing more harmful pollutants. You are unlikely to pass emissions checks as a result of this, along with the check engine light.

Before replacing your O2 sensors or catalytic converter, make sure you’ve ruled out any other probable sources of inefficiency in the catalyst system. Some automobile owners make the mistake of changing a perfectly good catalytic converter due to wiring or software problems. It is advisable to see a certified technician guarantee that you receive an accurate diagnosis and do not waste money on unnecessary component replacement.

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