Fix P0420 / P0430 OBD II Error code: Meaning, Symptoms, Causes & Solutions
The error codes P0420 or P0430 are raised due to a faulty exhaust system. In such a scenario, you get darker exhaust smoke, engine has rough idle with occasional stalling, and the check engine light is turned ON. Eventually, your scanner can also show fault code P0171/ P0174 or vice-versa.
What are Error Codes P0420 and P0430?
The trouble code P0420 and P0430 stand for Catalyst System efficiency below the threshold with P0420 for Bank 1 and P0430 for Bank 2. They are the same error raised for the same reason but different parts of the engine.
The issue is raised when the system detects a fault in the exhaust system, mainly the catalytic converter. The primary job of a catalytic converter is to filter the harmful contaminants out of the exhaust smoke before releasing it, when failed to do so, the error is raised.
Bank 1 and Bank 2:
Bank in an engine represents a cylinder bank or group of cylinders. A V6 has two cylinder banks or two groups of cylinders with 3 cylinders in each. Each bank has its own exhaust manifold connected to a separate catalytic converter. One is Bank 1 and another is Bank 2. Smaller engines with 3 or 4 cylinders only have Bank 1 with one catalytic converter.
To know which is Bank 1 or Bank 2 simply refer to the user manual or almighty Google.
Symptoms of P0420/P0430 error code:
When facing OBD II fault code P0420/P0430, you can face the following symptoms.
Blenching smoke: When the catalytic converter fails to filter the exhaust smoke, dirtier smoke would come out of your exhaust. It might smell like a rotten egg due to the presence of sulphur, would be darker in color and result in a failed emission test.
Check engine light: Check engine light would turn as the system detects a fault in the exhaust system.
Lack of power: Lack of power with poor engine performance, rough idling and stalling can all be caused by the P0420/P0430 error.
Bad fuel economy: Poor engine performance would also result in bad fuel economy.
What causes the Error Code P0420 and P0430?
The two main functioning parts of the exhaust system are the catalytic converter and oxygen sensor. So, when something goes wrong with the system, either one or both of them can be the culprit.
A Catalytic Converter goes bad when:
- There is a leak in the system: A converter can develop leaks in many areas due to many reasons. You can have leaks because of damage, due to rust or corrosion, bad fitting or deterioration.
The leak caused can reduce the exhaust’s backflow pressure, resulting in a sluggish, less efficient engine.
- Catalytic Converter is Clogged: A catalytic converter gets clogged due to coolant leak, oil leak, unburned fuel and engine contaminants clogging the interior of a converter. With the exhaust clogged, less air gets out, which means less air would get in. As a result engine stalling, lack of power and jerking gets common.
- The Converter has deteriorated: The catalytic converter is built to last around 50,000 miles. But how healthy your engine is determines how long the converter lasts.
The honeycomb structure inside the converter starts to break down as hot contaminants get stuck in it. The ceramic catalyst inside gets melted down due to unburnt fuel, hot oil or coolant. All resulting in a failing converter and P0420/P0430 error code.
A Oxygen Sensor fails when:
- Connection goes bad: The connection of an O2 sensor is direct to the ECU. When that connection fails, as if the wiring is open, short-circuited or burnt, the O2 sensor fails to give the necessary reading. This can cause the fuel to run too rich, resulting in more unburnt fuel and dirtier smoke.
- Develops contamination: An O2 sensor develops contamination over time due to rusting, leaking oil or coolant, leaded fuel, fuel additives etc. This may cause corrosion over the pins of the sensor, or cause contamination to build up, resulting in a false reading. Hence the error code P0420/P0430.
- Deteriorates over time: The Oxygen sensor can also deteriorate over time again leading to false or no readings, which can raise the fault code P0420/P0430.
How to fix error code P0420/P0430?
There are multiple ways you can go about fixing the fault codes P0420/P0430. But the first step is diagnosing the issue. The problem with that is the need for proper tools. To run an in-depth diagnosis you would need a scan tool to run checks on the CAT (catalytic converter) and O2 sensors.
Diagnosing the P0420/P0430 fault codes:
Running Dry checks on O2 sensor: There are several dry checks you can do to check whether your CAT and O2 sensors are fine. What you need to know is that generally, each exhaust system has two O2 sensors. One for the upstream flow and one for the downstream flow of the exhaust smoke. By the same logic, a car with two banks(two catalytic converters) would have four oxygen sensors.
Check each oxygen sensor one by one. First, see if they have loose/ cut wires or broken connections. Then unscrew each of them and see if the sensors are contaminated or corroded. If yes, replace them.
Running Dry checks on CAT: Look under your car to see if the exhaust system, that is exhaust pipe from the engine to the CAT, your CAT, and from the CAT to the outlet is damaged in any way. Turn on your car and see for smoke leaks. If yes, check if it's the cause of corrosion or bad fitting.
Diagnosing with Scan tool: Using a scan tool check for the upstream and downstream oxygen sensor values of each bank. Before that, make sure that your car is idling for 5 minutes first. For the upstream O2 sensor, the values would be constantly changing while it would be close to constant for the downstream. If the readings for both upstream and downstream are similar, your Catalytic converter is faulty.
Otherwise, you can remove your O2 sensor and run a simple diagnosis using a voltmeter to check if it's working.
Here's YouTube video provided by Ratchets And Wrenches to help diagnose an O2 sensor using a voltmeter, skip to 2:33.
Fixing the Error Code P0420/P0430
Once you figure out what is causing the issue, fixing gets a lot easier, possibly expensive as well.
Faulty oxygen sensor: If you have a faulty oxygen sensor, you most likely have to replace them. The cost of an Oxygen sensor ranges between $20-$100 (USD) while the replacement cost if done professionally goes up to $500.
Faulty catalytic converter (clogged): If your catalytic converter is faulty because it's clogged, you can most likely remove the clogging by yourself. Use a catalytic converter cleaner, pour it into a gas tank and use your car normally.
Another way to do it is by removing the converter and sinking it in a bucket full of detergent water. Leave it for about 8-10 hours and dry it out.
CAT can also be cleaned professionally if you are willing to pay around $100-$200.
Faulty Catalytic Converter(deteriorated): When a catalytic converter deteriorates, there is no fixing it. You most likely have to remove it and replace it with a new one. The issue is that the new converter ranges between $1000-$2500 or more depending on the make. As they have precious metal inside of them, they are expensive.
Alternate solution: One way to fix a bad catalytic converter causing the P0420/P0430 error code is to use an O2 sensor extender. By extending the O2 sensor, the readings can be altered, temporarily solving the P0420/P0430 fault code. One thing to note is that you will fail your emission tests and if caught, fines are expected.