OBD-2 Code P0420 Explained

OBD1 History: How Did It Come About?

P0420 is a trouble code for your vehicle. It is an OBD-2 code and stands for ‘Catalyst System Efficiency Below Threshold (Bank 1)’.

A P0420 Code identifies an issue with the catalytic converter in your vehicle in layman’s terms. This part of your vehicle is responsible for breaking down the harmful pollutants generated by the machine.

The catalytic convertor uses fine meshes made of platinum and steel to curb the flow of emissions from your vehicle. This device has a threshold of efficiency, which it cannot breach.

A P0420 Code notifies you when the efficiency of your catalytic converter has gone below the threshold.

Your catalytic converter has two oxygen sensors – the upstream one and the downstream one, pointed at the front and back of the actual converter, respectively.

When your vehicle is working correctly, the upstream oxygen sensor’s readings must fluctuate. However, the downstream oxygen sensor’s readings must be steady at the same time.

When these two sensors show similar readings, it can be interpreted that the catalytic converter is not working correctly.

Any such observation can be a P0420 Code, which will trigger your vehicle to prompt you to check your engine; it will flash the ‘check engine warning.

An experienced mechanic will use a special device called an OBD-2 (On-Board Diagnostics) Scanner to gather information from the oxygen sensors in the vehicle.


What Are The Causes Of a P0420 Code?

What Are The Causes Of a P0420 Code?

Like we stated before, any faults in the oxygen sensors attached to the catalytic converters can cause a P0420 Code.

These oxygen sensors can be damaged or have faulty wiring attached to them. Faults or damage to the catalytic converters is the most common cause of a P0420 Code.

One stark phenomenon leading to a P0420 Code is a misfire in the engine. A misfire is when one or more of the engine’s cylinders faces an incomplete or zero combustion.

However, this misfire will feel like hesitation or shaking to a driver when running.

Damage to the vehicle’s exhaust pipe arrangement or the muffler can also cause a P0420 Code. 

Also, if you are using the wrong fuel for your vehicle – led instead of unleaded – then you might face a P0420 Code.

What Are The Symptoms Of a P0420 Code?

What Are The Symptoms Of a P0420 Code?

Your vehicle will ordinarily find numerous ways to tell you an anomaly in its system.

Commonly, the ‘check engine’ signal on your dashboard will light up if there is a problem with the catalytic converter.

However, to figure out and decipher the source of the problem, a mechanic will have to use the special gear.

Another symptom you might notice in the case of a P0420 Code is that your vehicle will show a lack of power even after warming up significantly. Your vehicle might not accelerate in the usual manner.

If you drive on highways or freeways, your vehicle might not accelerate beyond 30-40mph (50-65 mph). It is a clear indication of some failure in the engine machinery and might warrant a P0420 Code.

If you notice a pungent smell emanating from the exhaust pipe of your vehicle, then it can be a symptom of a P0420 Code.

The pungent, rotten-egg-like odor can result from an incorrect amount of oxygen in the catalytic converter, leading to creating a layer of sulfur in the fuel tank.

Some of the symptoms might go unnoticed, other than the reasonably obvious ‘check engine’ flash sign.

While the P0420 code is not a very serious issue upfront, keeping it unchecked might create problems for the vehicle in the future. The catalytic converter might face severe damage if the P0420 code is ignored.

Mind you, replacing a catalytic converter is an expensive job. It can cause anywhere from $400-2400.

How Does a Mechanic Diagnose a P0420 Code?

An expert mechanic would use an OBD-2 scanner to shelf out trouble codes from the vehicle’s engine. It would give the mechanic a better idea about the anomalies in the car.

They would then study the data from the two oxygen sensors connected to the catalytic converter. It should paint a more accurate picture of the causes of the P0420 code.

The mechanic should also conduct multiple test drives to check the working of the downstream oxygen sensor. They should not replace the oxygen sensors before completing the diagnostic process.

If another component is causing the anomaly, then replacing the oxygen sensors will not solve the problem.

There is a chance that the P0420 code will appear for a few days and then disappear on its own. However, it would be unwise to ignore it because the problem may return in a few months.

Checking the warranty on your vehicle’s parts is a good option as the P0420 code returns persistently.

How To Handle a P0420 Code?

How To Handle a P0420 Code?

A P0420 Code is not the most severe problem with your vehicle. However, that does not mean it is unimportant. Keeping your vehicle duly maintained will reduce the possibility of this anomaly.

Replacing essential components on time is a foolproof way to safeguard your car against problems. For example, one must replace the car’s filter every 12,000-15,000 miles.

If you keep running your car with the P0420 code, then you might not pass some government-mandated pollution emission tests.

Getting your vehicle checked by an experienced mechanic is the best possible solution to this trouble code.

If you opt to change the catalytic converter, be sure to purchase machinery of the best quality possible.

It is because any aftermarket converters you buy will not be effective in the long run, and the P0420 code will not leave your dashboard. 

Moreover, it is essential to know that the P0420 code you observe may not exist in isolation. Since it is a part of OBD-2, it can pop up along with a slew of other trouble codes.

It is vital that the mechanic also checks for these trouble codes and the P0420 code.

Take good care of your vehicle, and stay safe.


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