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  • The P0430 code stands for “Catalyst System Efficiency Below Threshold (Bank 2).”
  • This trouble code is triggered when the computer detects a problem with the catalytic converter mounted near engine bank 2.
  • A faulty catalytic converter, damaged O2 sensor, wiring issues, and exhaust leaks are the most common reasons why the on-board computer can log a P0430.
  • If the computer logs a P0430 code, your vehicle can exhibit symptoms like an illuminated check engine light and a failed emissions test.

Your vehicle starts belching smoke. Its engine might stall, lose power, and idle roughly. Finally, the check engine light switches on. When you plug the OBD-II (on-board diagnostics 2) scanner into the connector, it shows the trouble code P0430.

What Does the P0430 Code Mean?

P0430 is a diagnostic trouble code (DTC) for “Catalyst System Efficiency Below Threshold (Bank 2).” It warns about a problem with the catalytic converter mounted near engine bank 2 (the side of the engine opposite the number one cylinder).

A failing catalytic converter breaks down less pollutants in the exhaust, resulting in lower oxygen (O2) levels overall. The downstream oxygen sensor detects the change and informs the vehicle’s computer. In turn, the computer activates the check engine light and logs the appropriate OBD-II trouble code for diagnosis by a trained mechanic.

In most cases, a vehicle with an inefficient catalytic converter will continue to run just fine. But if the converter is obstructed internally, it can cause poor engine performance and may even damage the engine in the long run.

Both scenarios can result in higher levels of pollution that may violate state and federal limits on vehicle emissions, although many states do not require emissions testing.

, P0430 Code: Catalyst System Efficiency Below Threshold  (Bank 2)

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Typically, the check engine light (CEL) will be illuminated before exhaust clogging becomes a problem, so find out why that light is on.

If the OBD-II code reader displays a P0420 or P0430 trouble code, bring your vehicle to an auto repair shop for a thorough checkup and repair job.

How the Catalytic Converter Works

The catalytic converter is an exhaust-mounted emissions control device. When working properly, it transforms pollutants created by the engine into harmless water vapor and carbon dioxide.

The three enemy gasses the emissions system targets are:

  • NOx (nitrogen oxides)
  • HC (hydrocarbons or unburned fuel)
  • CO (carbon monoxide, which is an invisible, odorless, and deadly poison in a closed space)
See also  P2096 Code: Post Catalyst Fuel Trim System Too Lean (Bank 1)

A “catalyst” changes other things without undergoing change itself. Today’s vehicles have what is known as a “three-way catalyst” that handles all three of the harmful gasses.

catalytic converter honeycomb
The catalytic converter has a hard clay “honeycomb” coated throughout with very fine particles of precious metals like platinum and palladium rhodium and surrounded by a vermiculite blanket. Those precious metals are the catalyst, and the converter must get very hot (over 1,000 degrees) before they begin to work. Most catalysts heat up very quickly and operate at around 1,400 degrees F. That’s why the “light off” catalyst is mounted so near the engine. | Image Source: Richard McCuistian

As for the P0430/420 codes, it’s important to note that these codes only point to a problem with the light-off converter that is mounted closest to the engine. The rear converter isn’t monitored by the OBD-II system. Some converters have both “bricks” in one shell with the oxygen sensor screwed right into the middle of the converter between the two bricks.

As for the P0430/420 codes, it’s important to note that these codes only point to a problem with the light-off converter that is mounted closest to the engine.

Richard McCuistian, ASE Certified Master Automobile Technician

The light-off converter nearest the engine handles NOx emissions (a product of hot combustion), while the one farthest from the engine handles HC and CO (from too-rich mixtures). An engine with a healthy catalyst system will produce CO2 and water vapor at the exhaust.

Remember, normal combustion creates water vapor, and that’s why all that steam comes from the exhaust until the exhaust system warms up when you start a vehicle in cold weather. An engine typically produces a gallon of water for every gallon of fuel consumed. Is this a problem? Not at all. Neither is CO2. The grass loves CO2, which is one of the reasons roadsides need so much mowing. CO2 feeds plants and trees exactly what they need.

But since 1996, OBD-II regulations have required the PCM (the vehicle’s engine computer) to keep track of the catalytic converter’s performance by monitoring the downstream oxygen sensor, which is referred to as such because it’s located behind the catalytic converter.

If you’re advanced enough to watch live data on a scan tool or with your smartphone app talking to a dongle connected to the DLC connector on a healthy engine, you’ll see the upstream O2 sensor the computer uses to balance the air/fuel mixture switching rapidly (several times per second). You’ll also see the downstream corresponding O2 sensor switching much slower.

That’s the way it’s supposed to be. When the downstream sensor begins to switch at the same rate as the upstream sensor, the P0420/P0430 codes are stored by the PCM to flag the failure of the catalyst to store oxygen.

P0430 vs. P0420

The P0430 code’s mirror image is P0420, which applies to the converter on bank 1. As was mentioned, bank 1 and bank 2 simply refer to the different sides of the engine. It’s also worth noting that engines with an inline or straight cylinder configuration only have one bank, although some inline six-cylinder engines will have two “banks” and two cats with four O2 sensors. Jeep 4.0L inline six-cylinder engines tend to be configured this way.

While the OBD-II scanner can distinguish between a P0420 code and a P0430, it never hurts to double-check for issues that may cause a problem with the catalytic converter. There can be different causes for vehicles like a BMW with code P0420 and P0430.

See also  Bad Catalytic Converter Symptoms: Signs to Watch Out For

What are the Possible Causes of the P0430 Code?

Close-up shot of a car's oxygen sensor
One possible cause of the P030 code is a damaged or failing oxygen sensor.

A faulty catalytic converter is the most frequent cause of a P0430 trouble code. Common issues that can cause this OBD-II code include:

  • Faulty catalytic converter.
  • Damaged or failing O2 sensor that gets incorrect readings of emission levels.
  • Broken or improperly connected wiring for the downstream O2 sensor.
  • Upstream and downstream O2 sensors reporting very similar O2 level readings. It’s important to note that if the upstream O2 sensor becomes unreliable and the PCM detects it, the downstream O2 sensor becomes the primary fuel feedback signal. Many mechanics don’t know this, but the PCM’s programming is all about keeping the catalytic converter happy. That’s how important the converter is.
  • An upstream leak in the exhaust system, such as a crack in the exhaust manifold or a loose header pipe at the manifold that allows air to enter and confuse the upstream sensor.
  • Faulty fuel injectors.
  • Computer issues (e.g., software in need of an update).
  • Engine isn’t heating up enough.

There are also several problems that can cause the catalytic converter to fail in the first place. Engine performance issues, such as a misfire or improper air/fuel ratio, can cause the converter to overheat due to raw fuel passing through the converter. This can make the converter glow cherry red in extreme circumstances.

The converter can also be damaged by contaminants (e.g., coolant and engine oil).

What are the Common Symptoms of the P0430 Code?

You may notice the following symptoms if you drive a vehicle with a P0430 trouble code:

Often, code P0430 indicates a converter that’s worn out or degraded, rather than obstructed internally. But if the converter is blocked or clogged, that can lead to engine performance problems, such as lack of power, rough idle, and stalling.

How to Diagnose the P0430 Code

There are numerous potential causes for the OBD-II code P0430. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the video below:

How to Fix the P0430 Code

There are multiple reasons why code P0430 might be stored. Therefore, there isn’t a magic bullet fix for the issue. You’ll need to diagnose the code accurately, as outlined above, then perform any necessary repairs.

The code could be triggered by parts like a bad catalytic converter, a faulty oxygen sensor, or a damaged wiring harness and connectors, so you must do your homework. If your scan tool is still showing p0420 and p0430 codes after replacing the catalytic converter, then a bad oxygen sensor might be the problem, instead of a bad catalytic converter.

Also, keep in mind that all vehicles are different. When troubleshooting and repairing DTCs, you should consult the factory repair information for your application.

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Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.

Other Notes About P0430

Since it is a generic powertrain code, the P0430 trouble code applies to most makes and models of vehicles manufactured from 1996 onward. The exact repair method may vary according to the type of vehicle, but in general, the fix for a P0430 on a Ford will be pretty much the same as the fix for a Chevy or Nissan. This fix might also work for a P0430 on a Lexus GS300, a P0430 on a Toyota 4Runner, or a Honda Odyssey P0430.

Many car owners make the mistake of immediately attributing a P0430 trouble code to the oxygen sensors and replacing the devices without checking for other possible causes. Since the problem will usually be the catalytic converter, another part of the exhaust system, or even the engine, simply replacing the O2 sensors is a waste of time and money.

Vehicle owners with extensive DIY auto repair can fix most issues that cause a P0430 trouble code. However, the safest approach is to bring the vehicle to an auto repair shop for diagnosis and repair.

Where To Buy Parts for the P0430 Code

If you’re looking to buy a new catalytic converter, O2 sensors, or other parts you need to resolve the P0430 trouble code, order now from! With our wide selection of aftermarket brands, you’re sure to find the part you need without breaking the bank.

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Products Mentioned in this Guide

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, P0430 Code: Catalyst System Efficiency Below Threshold  (Bank 2)
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About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Jason the Mechanic

This is some great information and I really was able to figure out what is really going on with the vehicle.

Thank you, Jason! We’re glad the information helped you fix your vehicle!

Jared L Dingus

Thank you for the info – my Rama Tuner just picked this code up – oh boy!

Phil Agree

Clear, concise, yet comprehensive. Well done.

Robert T Blaurock

I have replaced the sensors, converter, coils, plugs, checked exhaust leaks, purge valve and relearned the controllers. I still have the P0430 code pop up. Odd that it happened this morning after I relearned the throttle valve.


Would the cat cause other things like the throttle body to throw a code also?


i have had throttle replaced 2 times, egi harness, complete cat system, engine timed, and still jerks at about 20 to 25 miles. each time helps the problem but never fixes it and now after recall of CVT its passed milage to be claimed i find out it has a trans hissing. I am exhausted.

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