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Click below to watch the video and follow the steps to diagnose and fix your P0420 code. Keep in mind, the advice in this guide is general in nature. If you would like expert advice specific to your vehicle, as well as help completing at-home repairs, start your 100% free FIXD Premium trial now.
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The most common cause of a P0420 code is a worn catalytic converter, but this can differ depending on your specific model. These can cost over $1000 to replace, so before you replace it, make sure it really needs to be replaced. There are 4 main causes of P0420 that we need to check. Click on sections below to learn more about each possible cause.
FIXD Premium members can see the most likely repair and cost for their exact car in the FIXD app. If you want to access our Mechanic Hotline and see your most likely repair and cost, start your free FIXD Premium trial.
Difficulty Level: Beginner
Tools Needed: OBD2 Scanner
P0420 may not be your only code. Before you fix anything related to P0420 make sure you don’t have any other error codes because they could be the cause of your P0420. For instance, if a P0300 (cylinder misfire) or P0172 (too much fuel in air/fuel mixture) can cause a catalytic converter to fail. If you replace your catalytic converter without fixing the root cause, your new catalytic converter will fail too.
The only way to know if you have other codes is to use an OBD2 scanner. There are a few options for this:
Pros: The main benefit of this is that you get your answer for free. They will scan your car and let you know all of the codes on your car.
Cons: The downside is they won’t tell you what is causing your error codes. You’ll still have to go to a mechanic or figure that out for yourself. If you want them to clear your check engine light, they might not be willing to do that for liability reasons.
Pros: A mechanic will be able to scan your car and will be able to figure out what is the root cause of your problems and fix it. Mechanics usually charge about $100 for a diagnosis, but they typically deduct this cost from your bill if you get them to fix the problem too.
Cons: This is probably the most expensive option. Not only will you pay for the parts, but you’ll have to pay for labor.
Pros: With FIXD you’ll be able to scan your codes yourself. You’ll also be able to read live data from your car’s sensors to diagnose your problems. If you need any help or expert advice you can call the FIXD Mechanic Hotline for free to get specific answers for your car’s problems.
Cons: FIXD is free for the first 14 days of membership, which should be enough time to fix your car with the help of our on-call mechanics. Click here to try FIXD Premium for free.
Difficulty Level: Beginner
Tools Needed: Jack Stand Or Ramps
Exhaust leaks can cause P0420 codes and are relatively easy to identify. Before you start, make sure your car has been off for several hours or you can get burned by the exhaust system. You may need to raise your car on stands or ramps to access your exhaust system. Leaks can happen at the exhaust manifold flange, O2 sensor threads, pre- and post-cat exhaust clamps, and any obvious damage to the catalytic converter itself. There are a few methods you can try at home to find exhaust leaks.
Exhaust leaks have a distinctive sound. Listen for a sputtering noise shown in the video below.
You can usually spot leaks as excessive black carbon buildups that are usually formed at a junction in the exhaust pipe. Make sure to check the catalytic converter and O2 sensors, including the wiring. If you can hear a rattle when knocking on the catalytic converter or if you can see obvious damage to the O2 sensor wiring, you should start by addressing these issues first. Damaged wiring might be burned, smashed, exposed, or completely severed.
If you’re not sure you found a leak or need advice, a FIXD Mechanic can work with you to find a leak. You can call FIXD mechanics for free when you’re a member of FIXD Premium. Click here to try FIXD Premium free for 14 days!
Difficulty Level: Beginner (With FIXD) – Advanced (With Multimeter)
Tools Needed: FIXD Sensor Or Multimeter/Butane Torch
Your exhaust system has two O2 sensors (oxygen sensors), one before the catalytic converter (O2 Sensor 1) and one after the catalytic converter (O2 Sensor 2). If they are working properly O2 sensor 1 should constantly fluctuate between 0.1V – 0.9V and O2 sensor 2 should be steady. Checking your O2 sensors will tell you if you need new O2 sensors or a new catalytic converter. If you can’t get a reading from your O2 sensors it means you need to replace the sensors. If the sensors are functioning and displaying unexpected readings, the catalytic converter might be worn. There are two ways to check your O2 sensors.
The easiest way to read your O2 sensors is by using FIXD. The FIXD Sensor plugs into your OBD2 port (usually under your steering wheel) and reads live data from your car’s sensors (see image below for example of O2 sensor 2 reading from FIXD app). Simply go to the “Live Data” tool in the FIXD app and pull up your O2 sensors. If you can’t get a reading from your sensors it means your sensors may be damaged. If your O2 sensor 2 reading is fluctuating like O2 sensor 1 it means your catalytic converter is bad and needs to be replaced. You get a free FIXD Sensor when you become a FIXD Premium member. It’s completely free to try FIXD Premium for 14 days, which should be enough time to fix your car with the help of our on-call mechanics. Click here to try FIXD Premium for free.
This is a more advanced method. You’ll first have to remove your O2 sensor from your car. Using a digital multimeter and butane torch, measure the sensor’s voltage as you heat up the element. If the voltage doesn’t get within 0.1V – 0.9V you have a bad O2 sensor and need to replace it. See the video below for guidance.
Before you fix P0420, make sure you correctly diagnose the cause of the code first. If you don’t, you could end up spending $1000s buying a new catalytic converter when that wasn’t the cause of the code. Below are some of the main causes of a P0420 code. Click on sections below to learn more about each repair.
Difficulty Level: Intermediate
Tools Needed: Tail Pipe Expander, Exhaust Couplers, Exhaust Clamp, Exhaust RTV
If you’ve found the leaks in your exhaust the next step is sealing them. You can do this with a welder, but if you don’t have one, there are other ways. The easiest alternative is to simply remove the damaged length of the exhaust and replace that length with an exhaust coupler. Watch the video below to see how it’s done.
If you need advice, a FIXD Mechanic can work with you to fix the leak. You can call FIXD mechanics for free when you’re a member of FIXD Premium. Click here to try FIXD Premium free for 14 days!
Difficulty Level: Intermediate
Tools Needed: O2 Sensor Socket, New O2 Sensor
If you find your O2 sensors are broken and need to be replaced, you can do this yourself. You will need an O2 sensor socket to remove the old sensor and install the new one. An O2 sensor socket is a 22mm socket that is designed to not get in the way of the wires coming out of the O2 sensor so you don’t damage the new O2 sensor. Watch the video below to see how it’s done.
If you need advice, a FIXD Mechanic can work with you to replace the sensor. You can call FIXD mechanics for free when you’re a member of FIXD Premium. Click here to try FIXD Premium free for 14 days!
Difficulty Level: Intermediate (with direct fit catalytic converter) – Advanced (with universal fit catalytic converter
Tools Needed: New Catalytic Converter, Socket Wrench, Penetrating Oil
Catalytic converters can be relatively easy to replace depending on what type they are. Direct fit catalytic converters are designed specifically for your car and will bolt right into your exhaust system. Direct fit catalytic converters can be expensive because they are made to fit one model. Universal fit catalytic converters are cheaper and are designed to fit a wide range of cars. You will have to custom fit a universal catalytic converter into your car. If your goal is to save money and you aren’t afraid to work on your car, you should consider a universal fit catalytic converter. Watch the video below to learn how to replace your catalytic converter.
If you need advice or help, a FIXD Mechanic can work with you to place a new catalytic converter. You can call FIXD mechanics for free when you’re a member of FIXD Premium. Click here to try FIXD Premium free for 14 days!
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