Jeep P0420 – Engine Code Solution – Catalyst System Efficiency Below Threshold

What does the Jeep code P0420 mean?

Code P0420 stands for “Catalyst System Efficiency Below Threshold.” This is a warning sign from your jeep trying to tell you there’s something unusual going on in the catalytic converter.

Let me explain what the catalytic converter does without getting too technical.

It transforms pollutants your jeep generates into less harmful gases that can be released into the environment.

Jeep Code P0420

  • Catalyst System Efficiency Below Threshold

Causes of code P0420

  • Faulty oxygen sensor
  • Worn out catalytic converter

Symptoms of code P0420

  • Engine light is on
  • Poor fuel economy
  • Rotten odor
  • Lack of engine power

Fixes for code P0420

  • Replace the oxygen sensor
  • Repair or replace the catalytic converter

Your car’s computer will keep an eye on this process by using two oxygen sensors.

The first one reads the oxygen amounts before the pollutants go into the catalytic converter; the second one reads the oxygen amounts after the pollutants come out of the converter. Simple!

When the first sensor and the second sensor get similar readings, your car notices something is wrong (if the oxygen amount is the same before and after the process, the converter is not doing its job) – and that’s when you get the P0420 engine code.

You can probably guess that, in this scenario, you either have an issue with your oxygen sensors or your catalytic converter.

There’s also a small chance that a leak in the exhaust system is causing the issue, but you should check that after you make sure both the oxygen sensors and the converter are working properly.

What can cause an oxygen sensor to go bad?

You usually have 100,000 miles (give or take) before an oxygen sensor breaks. Unfortunately, you can wear out this sensor earlier than usual if you put poor-quality fuel in your gas tank. Not keeping up with regular car maintenance can have similar results.

So, how can you tell if you have a worn-out oxygen sensor or a faulty catalytic converter? The answer is simple: you can smell it.

That’s right. When you have a worn-out oxygen sensor, your exhaust will smell terrible. It’ll be as if there’s something rotten coming out of it.

Other than that, you can use your scan tool to check it out. Your scan tool will tell you which sensor went bad when you plug it in almost every car model.

How do I fix an oxygen sensor?

When an oxygen sensor goes bad, you need to replace it. You can’t repair it. An average oxygen sensor can cost you from $200 to $400 if you take your car to the repair shop.

You can save a little money if you replace the sensor yourself. There’s a little issue with that, though.

The oxygen sensor is located under your car – and you may have a hard time reaching there unless you know what to do (and have the tools to do the job).

Replacing the sensor is easy. It’s almost like unscrewing a light bulb.

Then again, as I’ve said, the hard part is getting to where the sensor is – and that little location varies in every car model. A mechanic will know how to do it, though.

What can cause a catalytic converter to fail?

There are a lot of things that can kill your catalytic converter. It could be overuse, high temperatures, faulty parts (like a malfunctioning spark plug), and more. At the end of the day, once the converter fails, it’s time to replace it – no matter the reason.

Truth be told, neglect is what breaks a catalytic converter.

Not paying attention to the engine light, using poor coolant, and neglecting the yearly maintenance routine (remember to do a checkup once a year or every 10,000 miles!) will put enough stress to break a converter.

It could also be bad luck, though. Sometimes, things just break – and a converter is no exception.

How do I fix a catalytic converter?

You can try to salvage your catalytic converter before you decide to replace it. You may save yourself some money if the problem is a clogged converter and not a damaged one, so make sure you check for obstructions and leaks in there.

Cleaning your converter with a power washer or soaking it overnight with water and a degreaser could save it. If that doesn’t work, you need to replace it.

A catalytic converter costs anywhere from $500 to $2000 – so try to salvage it before you decide to break the bank and get a new one.

Do I have a leak in my exhaust system?

If you have no issues with your oxygen sensors or the catalytic converter but still get the code P0420, you have a leak in the exhaust system. More often than not, exhaust issues cause engine noises and gas pedal vibrations.

Yes, I know. There’s no need for you to say it.

The oxygen sensors and the catalytic converter are a part of the exhaust system. In this article, when I’m talking about the exhaust system, I’m talking about everything but those two parts.

And it could be almost anything once you rule out the sensors and the converter.

So, at this point, there are one too many moving parts for me to help you without doing an inspection myself.

I’d recommend taking the car to a repair shop or taking the time to check the exhaust system entirely and see what’s wrong.

Is code P0420 serious?

You shouldn’t overlook the P0420 code under any circumstances. While a faulty oxygen sensor may not cause too much trouble, a malfunctioning catalytic converter or exhaust system are trouble enough to cause worry.

Will you have engine issues with a code P0420 right away? Well, not right away – but leave it unattended, and it could cause more serious damage to your car.

Having this engine code could affect your car’s drivability and fuel economy, so you’re going to have a hard time getting from point A to point B – and that’s not what you want either.

You can postpone fixing the code 0420 for a couple of days at best, but not longer than that.

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