P0430 – Catalytic converter system, bank 2 -efficiency below threshold

By Ti (Contact Me)
Last Updated 2023-03-13
Mechanical Engineer
CodeFault LocationProbable Cause
P0430 Catalytic converter system, bank 2 -efficiency below threshold
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Catalytic converter, wiring, HO2S 2

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Table of Contents

  1. What Does Code P0430 Mean?
  2. How do you troubleshoot code P0430 ?
  3. Get Help with P0430

What Does Code P0430 Mean?

The P0420 and the P0430 codes are caused by catalyst inefficiency.  Replacing your catalytic converter is costly, so, knowing if a new catalytic converter is needed pays off.

Your car’s exhaust system (below) comprises: a catalytic converter (s), at least two oxygen sensors and exhaust pipes that route the engine’s exhaust from the engine, through the catalytic converter, and out the car.  The oxygen sensors sample your car’s exhaust before and after the catalytic converter.  In response to the amount of oxygen found in the exhaust, the oxygen sensors output a voltage which can be read with a multi-meter, oscilloscope, or scan tool.  The oxygen sensor upstream of the catalytic converter will normally be referred to as Bank 2 O2 Sensor 1 (B2O2S1) and the downstream oxygen sensor will be Bank 2 O2 Sensor 2 (B2O2S2).

O2 Sensor Bank 1 Bank 2

Oxygen Sensor

Zirconia oxygen sensors are the most common type of sensor found in cars.  The sensor measures the difference in oxygen present in atmospheric air (outside air in the figure below) and the oxygen present in the exhaust gas.  The percentage of oxygen in the atmosphere is 21% and the exhaust gas oxygen can vary between 0% (rich condition) and 2% (lean condition).  The oxygen sensor’s voltage output, which is read by the car’s computer, will decrease in a lean condition and increase in a rich condition.

Oxygen Sensor

A normal reading for an oxygen sensor will fluctuate sinusodially between 900 millivolts (rich condition) and 100 millivolts (lean condition).  Why does the amount of oxygen vary if the car is functioning properly?  Doesn’t the computer always maintain a constant stoic metric mixture of fuel and air?  There are two reasons: (1) catalytic converter efficiency increases when the exhaust gas mixture is either slightly rich or slightly lean so the car’s computer purposely varies the combustion mixture to increase and decrease the oxygen remaining post combustion (2) the oxygen sensor acts like a switch and is either “on” or “off” in response to very small changes in the air fuel ratio.

O2 Sensor Voltage Graph

Oxygen sensor waveforms can exhibit “hash” or high frequency oscillations which are much more rapid than rich lean oscillations.  It is important to identify the difference between hash caused by misfires and signal noise.  Team ZR-1 has an excellent post on “hash”: http://www.teamzr1.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=1458

Catalytic Converter

The catalytic converter changes the chemical composition of the exhaust gas mixture.  A good catalytic converter will cause the oxygen in the exhaust to react with any hydrocarbons creating water and carbon dioxide.  The important thing to remember for the P0430 trouble code is that there should be no oxygen remaining in the exhaust mixture downstream of the catalytic converter.

How do you troubleshoot code P0430 ?

A functioning exhaust system should have a precatalytic converter oxygen sensor reading that varies sinusodially between 100 millivolts and 900 millivolts and a downstream oxygen sensor (oxygen sensor after the converter- see below) reading which is constant above 600 millivolts.  If your oxygen sensors show this behavior then the catalytic converter is efficiently converting all the oxygen in the exhaust.  The constant high voltage from the oxygen sensor after the converter tells us there is no oxygen post catalytic converter.

Oxygen Sensors & Cat

How do I know that my catalyst is bad? Will a bad oxygen sensor or exhaust leaks trigger the P0430 code?  If both your oxygen sensors show identical sinusodial readings, it is very unlikely anything other than a bad catalyst is the cause.  No combination of exhaust leaks can duplicate downstream and upstream sinusoidal oxygen sensor readings.  Described below is a propane test which will verify your catalytic converter is bad.

IMPORTANT: Remember that when testing oxygen sensors the car must be warmed up.  You will not get any oxygen sensor readings if you have just started your car…

Troubleshooting Exhaust Systems with Air-Fuel Sensors

Many newer cars do not have traditional oxygen sensors.  Instead the car industry has transitioned to air-fuel sensors or wideband oxygen sensors.  One of the first manufacturers to make the change was Toyota.  Since 2006, Toyota’s cars have wideband oxygen sensors.

Air-fuel sensors or wideband oxygen sensors are significantly different from traditional zirconia oxygen sensors.  The output of an air-fuel sensor will be a constant value – gone are the varying sine waves of the oxygen sensor.  Another difference is the air-fuel sensor’s response to fuel.   An air-fuel sensor will decrease its output voltage for a rich condition and increase its output for a lean condition.  This is the opposite of zirconia oxygen sensors!

The strange behaviour of these air-fuel sensors is caused by the underlying sampling of the air fuel mixture.  Whereas, the traditional oxygen sensor could only detect a rich or lean mixture and not the degree of richness or leanness, a wideband oxygen sensor calculates the air fuel ratio with precision.  The wideband sensor output for a 15:1 air fuel ratio will be different than the output for a 20:1 air fuel ratio.  With traditional zirconia oxygen sensors both these ratios would be lean and the resulting output would be the same – a low voltage of 100 millivolts.

If you would like to know more about the physical differences between the two sensors, Clemson University has an excellent article with figures including Nernst and Pump cell structures: http://www.cvel.clemson.edu/auto/sensors/oxygen.html

Catalytic Converter Propane Test

Introducing propane into the car air intake will aid diagnosing the catalytic converter and O2 sensors.  To run this test the car should be warmed up and running in a closed loop.

1.  Connect the scan tool

2.  Set the scan tool to monitor the upstream and downstream O2 sensors and the short and long term fuel trims

3. With the car running, introduce propane into the air intake (all your  O2 sensors should respond with a high steady voltage)

Oxygen Sensor with Propane Response

4.  Keep adding propane until the short term fuel trim is over -20%

5.  Once a rich condition is reached (step 4), stop adding propane

6.  Obtain a freeze frame of the O2 sensor response to the removal of propane

7. Analyze the O2 sensor response

Remember, a properly functioning catalytic converter will remove O2 from the exhaust gas.  If your catalytic converter is doing its job, there will be a delay of more than 1 second in the downstream O2 sensor’s transition from the rich condition to the very lean condition caused by the propane test.  If both the upstream and downstream O2 sensor respond immediately to the removal of propane by going lean, your catalytic converter is bad and is not removing O2 and hydrocarbons efficiently.

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