1A Auto Video Library
Our how-to videos have helped repair over 100 million vehicles.

Check Engine Light Catalyst System Efficiency or Bad O2 Sensor - Code P0420P0430

Share on:

Check Engine Light Catalyst System Efficiency or Bad O2 Sensor - Code P0420P0430

Created on: 2018-11-26

If you have a check engine light code P0420 or P0430 there may be a problem with your catalytic converter. But sometimes, the problem could be the oxygen sensor that takes readings from the catalyst. Watch this video to find out the difference

  1. step 1 :What Code P0420 Means
    • P0420 could mean too much of the filter in the catalytic convertor is clogged

Tools needed for replacement

  • 1A - No Tools Needed

    No Tools Needed

Installation Video
Watch video

Hi. I'm Mike from 1A Auto. We've been selling auto parts for over 30 years.

Hey, everyone. Sue here at 1A Auto. And today I'm going talk quickly about oxygen sensors. Problems of people that get the code and they don't understand it. So, I'm just gonna break it down in quick laymens terms, so you feel like you're not being taken if your mechanic tells you have O2 sensor code. So, I have an exhaust system set up here. This is for a Subaru, and you have the converter is right in here. There's a little honey cone mesh in here. This filters out the carbon monoxide that comes out of the engine, and comes down to this pipe and goes out to through the muffler. So, this is what we would call a downstream O2 sensor, because it's after the converter--the honey cones. And this would be a upstream. In this case, this would be considered an air:fuel ratio sensor.

So, the computers are connected to these, and this gives sensors back to the computer. Gives it awareness. See the little vented holes? That's like a sniffer. So, it's like an ant eater inside that exhaust. And it's constantly taking messages. Taking messages and sending it to the ECM. And when your converter is clogged, the downstream one will pick up a limited amount of carbon monoxide. And it says, "Hey, somethings going on here. We're not smelling anything." So, it sends a Cat Efficiency code, P0420. That means this is doing its job, you don't need to replace this unless it's extremely old and you're going to replace the exhaust anyways, then I would do it. But, don't say, "Oh, I'm going to replace this, and that's going to take care of the code." Don't condemn this for doing its job. Cat Efficiency code, it's working. It means that inside here, that honey cone is filtering properly.

Thanks for watching. Visit us at for quality auto parts, fast and free shipping, and the best customer service in the industry.

Tools needed for replacement:

    1A - No Tools Needed

  • No Tools Needed

Search Videos
Go To Top

Same Day Shipping

Need your part faster? Choose expedited shipping at checkout.

Guaranteed To Fit

Highest quality, direct fit replacement auto parts enforced to the strictest product standards.

USA Customer Support

Exceeding customers' expectations, our team of passionate auto enthusiasts are here to help.

Instructional Video Library

Thousands of how-to auto repair videos to guide you step-by-step through your repair.