Interpret and Fix OBD‐II Code P0420

If you ran a diagnostic and came up with OBD II code P0420, don’t panic. The problem most likely lies in your catalytic converter, which means you may be able to fix it yourself without even removing it from your vehicle. But first you will need to identify exactly where the issue is before you can take care of it.

Steps

  1. Check your exhaust system for leaks. Before doing anything else, you should check to make sure there is not a leak in your exhaust system somewhere. If there is, there may be nothing wrong at all with your catalytic converter. In order to check this, duct tape a vacuum cleaner to the exhaust pipe so that it’s airtight. Use a stethoscope and listen for leaks once you turn it on. If there are any, you will be able to pinpoint where they are by listening carefully.
  2. Check for a faulty oxygen sensor. If one of your oxygen sensors isn’t functioning the way it should, that could be the cause of your error code. You can check them by attaching a voltmeter to the feedback wire, and ground. Set it to millivolt, and then start the engine. Let it idle for around 15 minutes. The voltmeter’s indicator should read approximately 150 millivolts. If the needle bounces, that’s fine as long as it stays somewhere around 150.
  3. Pull the throttle and observe the indicator. It should go down for a fraction of a second then rise for a fraction of a second. Then it should return to around 150 again. If the indicator on the voltmeter does anything other than this, you have a faulty oxygen sensor and you need to either get it replaced or have it fixed.
  4. Use Catalytic Converter Cleaning Solution. If you don’t have any leaks in your exhaust system or a faulty oxygen sensor, then there has to be something wrong with your catalytic converter. That doesn’t mean that you will definitely have to replace it though. You may be able to give it a good cleaning to get it back into working order.
  5. Pour a full bottle of catalytic converter cleaner into your gas tank, and then drive your vehicle until the tank is empty. After you fill your tank back up with gasoline, you may see an improvement in the way it runs. More importantly, the cleaning should reduce the amount of air pollution your vehicle causes when you drive and allow you to pass an emissions test.

Tips

  • If that doesn’t work, you can wash your catalytic converter by hand. Dealing with rusted exhaust fasteners isn’t pleasant, but you should be able to remove it yourself and give it a cleaning. Alternatively, you could buy a new one and either install it yourself or hire a mechanic to do it for you.

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References