P0432 – Main catalytic converter, bank 2 -efficiency below threshold

Reinier

By Reinier (Contact Me)
Last Updated 2017-11-07
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0432 Main catalytic converter, bank 2 -efficiency below threshold Catalytic converter, wiring, HO2S 2

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What Does Code P0432 Mean?

OBD II fault code P0432 is a generic code that is defined as “Main Catalyst Efficiency Below Threshold -Bank 2”, and is set when the PCM (Powertrain Control Module) detects that the efficiency of the catalytic converter on Bank 2 has fallen below a minimum allowable level. On engines with two cylinder heads, “Bank 2” refers to the bank of cylinders that does not contain cylinder #1.

The purpose of a catalytic converter is to reduce harmful exhaust emissions to less noxious substances through a process of oxidization that depends on a variety of precious metals in the converter being at very high temperatures. When the exhaust stream passes over or through the precious metals, aka, the catalysts, a complex series of chemical actions and reactions convert especially oxides of nitrogen into harmless substances like oxygen and water.

However, while catalysts are not consumed in the conversion process, there are many factors relating to normal  (or sometimes abnormal) engine operation that can either shorten the useful life of a catalytic converter, or damage it to the point where it no longer works as intended, with serious negative effects on fuel economy and the environment.

Therefore, to monitor the efficiency of the catalytic converter(s) on any application, the PCM uses input data from (among other sensors), both the upstream and downstream oxygen sensors (or on some applications, the air/fuel ratio sensors). In a fully functional system, readings from the upstream oxygen sensor fluctuate greatly several times per second because it reacts to changes in the oxygen content of the exhaust stream, while readings from the downstream sensor remain fairly constant, provided the catalytic converter is operating at a high level of efficiency.

In practice, the PCM compares the input data it receives from the up -, and downstream sensors continuously, and if it detects that the readings from the downstream sensor matches those from the upstream sensor too closely, it uses the compared input data to calculate an efficiency level for the affected catalytic converter. If this calculated value falls below a preset minimum value, the PCM will set code P0432, and illuminate a warning light as a result.

Where is the P0432 sensor located?

Catalytic converters are fitted into the exhaust system ahead of the mufflers, which it resembles. The diagram below shows the typical arrangement of catalytic converts in an exhaust system fitted to a V-Type engine.

What are the common causes of code P0432 ?

The most common causes of code P0432 are many and varied, but could include the following-

  • Catalytic converter failure due to long use
  • Premature failure of rebuilt or refurbished catalytic converters
  • Failures and/or malfunctions in almost any system, sensor, or component that affects/controls/monitors/regulates combustion, and therefore, exhaust emissions
  • Use of unsuitable or poor quality fuel
  • Exhaust leaks in exhaust components such as exhaust manifolds, down pipes, balancing tubes, flexible hoses/pipes, and mufflers
  • Restrictions anywhere in the exhaust system that prevents or inhibits the free flow of exhaust gas
  • Mechanical issues in the engine, such as excessive wear of cylinders/piston/piston ring/valve gear that cause excessive oil consumption
  • Use of enhanced or unauthorized PCM programming
  • Unauthorized or illegal exhaust system modifications or alterations
  • Failed or failing PCM. Note that in the case of code P0432, this is an exceedingly rare event and the fault must be sought elsewhere before any control module is replaced

How expensive is it to fix code P0432 ?

As a general rule, the cost of a catalytic converter replacement runs to about $2000, parts and labour included. Note though that this estimate does not include taxes and fees that may be payable, nor does it include the cost of resolving underlying issues that may have contributed to the failure.

WARNING: Be aware that while rebuilt catalytic converters can be had for a fraction of the cost of an OEM grade unit, the savings thus made is a false economy, since the “rebuilt” converter can fail at any time, and usually within the first few thousand miles of use.

What are the symptoms of code P0432 ?

Some common symptoms of code P0432 could include the following-

  • Stored trouble code, and an illuminated warning light
  • Depending on the root cause of code P0432, other codes relating to misfires, fuel pressure, engine temperature, oxygen or air/fuel ratio sensors, and others may be present
  • Vehicle may not pass an emissions test
  • Hard, or no start conditions may be present if the catalytic converter had suffered significant damage
  • Depending on the degree of damage suffered by the converter, the engine may idle roughly or not at all, or the engine my exhibit varying degrees of power loss, particularly upon acceleration
  • Fuel consumption may increase considerably in some cases
  • In some cases, and especially where the converter had suffered significant damage, the converter may overheat to the point where it can set the vehicle on fire
  • In many cases, but depending on the nature of the problem, there may be no discernible symptoms apart from a stored code and an illuminated warning light

What are common solutions to code P0432 ?

Common solutions to code P0432 could include the following-

  • Resolving all possible underlying conditions that could affect exhaust emissions- refer to the “Common mistakes” and “Causes of code P0432” sections of this guide for more details.
  • Restoring PCM programming to stock
  • Removing unauthorized or illegal exhaust system modifications
  • Replacing substandard rebuilt catalytic converter(s)
  • Removing restrictions from the exhaust system

How serious is code P0432 ?

Code P0432 should be considered as serious even in the absence of obvious driveability symptoms, since the root cause of the code is not always immediately apparent. If left unresolved, this code has the potential to cause serious, if not fatal damage to the catalytic converter, which in turn, could set the vehicle on fire. Ideally, the vehicle should not be driven until code P0432 had been resolved.

How safe is it to still drive the car with code P0432 ?

As stated above, applications that display code P0432 should not be driven due to the distinct possibility that the vehicle could be immobilized unexpectedly, or worse, catch fire.

How difficult is it to repair code P0432 ?

Diagnosing this code should be well within the capabilities of most non-professional mechanics, provided a scanner that can monitor live data streams is available, and that there are no other codes present.

However, if the application uses air/fuel ratio sensors and additional codes relating to these sensors are present, an oscilloscope and a waveform library might be required to diagnose the cause of the sensor failure(s). If such equipment is not available, the better option would be to refer the vehicle to the dealer or other competent repair shop for professional diagnosis and repair.

NOTE #1: Bear in mind that while diagnosing this code might not be too difficult, replacing a catalytic converter requires partial or sometimes complete disassembly and/or removal of sections of the exhaust system, as well as some cutting and welding of the exhaust system. This is generally very difficult to do unless a vehicle hoist is available to be able to gain access to the exhaust system.

NOTE #2: Air/fuel ratio sensors and oxygen sensors work on vastly different principles, and while oxygen sensor faults can often be diagnosed with nothing more than a digital multimeter, diagnosing defective air/fuel ratio sensors requires the use of an oscilloscope, or professional-grade diagnostic equipment that incorporates an oscilloscope.

NOTE #3: An infrared or laser based thermometer is a required item when diagnosing this code, since the efficiency of a catalytic converter is closely related to its temperature when the system is operating in closed loop mode.

NOTE #4: One other essential item required to diagnose this code accurately is an exhaust gas pressure gauge that is designed to register up to 10 PSI, and is graduated in the smallest possible increments for increased accuracy. This gauge is required to measure exhaust back pressure as a diagnostic aid, but make sure that the gauge is provided with a fitting that will screw into the exhaust in place of the oxygen or air/fuel ratio sensor(s).

What are the common mistakes when repairing code P0432 ?

Mistakes made when diagnosing this code commonly include the following-

  • Not verifying whether oxygen or air/fuel ratio sensors are in fact defective, or operating correctly before replacing them. These sensors are very often replaced in error when the root cause of the code can involve failures and/or malfunctions in almost any system, sensor, or component that affects/controls/monitors/regulates combustion, and therefore, exhaust emissions.
  • Failing to resolve additional codes in the order in which they were stored. In fact, it is rare for code P0432 to appear by itself, and especially if the application is fitted with an OEM catalytic converter that is less than 100 000 miles old, which distance represents the federally mandated warranty period of OEM catalytic converters.
  • Failing to verify whether the affected catalytic converter on the application is an OEM unit, or a “rebuilt” unit. While refurbished catalytic converters are much cheaper than OEM units are, these rarely if ever, provide the same durability or efficiency as OEM equipment.
  • Failing to verify that the application’s PCM is not running on unauthorized or so-called “performance” settings. “Performance tunes” almost always result in over-fuelling conditions that stock catalytic converters are not designed to deal with over extended periods.
  • Failing to ensure that the engine is in perfect running condition. Before attempting to diagnose/repair this code, it is essential to ensure that there are no misfires, engine vacuum leaks, exhaust system leaks, clogged or damaged mufflers, excessive oil consumption, or other issues present that have negative impacts on the combustion process, or on the engine’s overall operation.

How do you troubleshoot code P0432 ?

NOTE: Before starting a diagnostic procedure for this code, check to see if the affected catalytic converter is still covered by the federally mandated 100 000-mile warranty. If it is covered, refer the vehicle to the dealer to discuss repair/replacement of the converter under warranty conditions.

Step 1

If the converter is not covered by warranty, record all fault codes present, as well as all available freeze frame data. This information can be of use in tracing the root cause of the code in cases where multiple additional codes are present.

NOTE: Refer to the “Common mistakes” section of this guide for more details on the possible causes of code P0432. If other codes are present, both active and pending, be sure to resolve all additional codes strictly in the order in which they were stored to avoid a misdiagnosis, and the possible unnecessary replacement of a hugely expensive catalytic converter.

Step 2

If no additional codes are present, clear code P0432, and operate the vehicle normally for a few miles to allow the PCM to enter closed loop operation, before scanning the system again to see if the code returns.

NOTE: “Closed loop” operation refers to a condition in which the PCM uses feedback data from the oxygen or air/fuel sensors to control fuel delivery.

Step 3

If the code persists, jack the vehicle up off the ground, and use properly rated jack stands to support the vehicle. This is required to gain (relatively easy) access to the catalytic converter. Once the vehicle is supported safely, start the engine and allow it to idle.

Use the scanner to monitor the operation of the oxygen or air/fuel ratio sensors to verify that all sensors are working as intended. Compare the displayed output signals from the sensors with the values stated in the manual as a double check to ensure that the sensors are not contributing to code P0432.

NOTE: Step 3 assumes that there are no additional codes present, as well as that additional codes that were present had been resolved and cleared, and can therefore no longer influence or affect the operation of the catalytic converter.

Step 4

Once it is certain that the PCM is in closed loop operation, use the thermometer to obtain a reading of the converter’s temperature, but bear in mind that most converters will only start to function at between 400 deg F and 600 deg F (204 deg C and 315 deg C).

If the observed reading falls within this range, have an assistant increase the engine speed to 2 500 RPM, while you are monitoring the converter’s temperature. If the converter is functioning correctly, its temperature will rise as the composition of the exhaust gas changes, but note that the converter is defective if its temperature approaches, or exceeds 2 000 deg F ( 1 100 deg C).

NOTE #1: The normal operating temperature of a functioning catalytic converter is between 1 200 deg F and 1 600 deg F (650 deg C and 870 deg C).

Next, obtain a temperature reading at the inlet of the converter, and then at the outlet. If the engine is in perfect running condition and there are no unresolved additional codes present, the difference between the inlet and outlet temperatures should generally well below 100 deg F (37 deg C). Note though that on many applications, and especially those with multi-point injection systems, this difference may be all but undetectable with DIY equipment.

However, if the temperature difference approaches or exceeds about 200 def F (93 deg C), or goes as high as 500 deg F (260 deg C), it is likely that the converter has suffered damage caused by the long-term effects of one or more underlying conditions, even if there were no additional codes present at the time that code P0432 appeared.

NOTE: A common clue of catalytic converter overheating is a deformed or discoloured converter shell. However, note that code P0432 can appear even if the converted has never overheated, such as in cases where the converter is no longer operating at peak efficiency due to long use.

Step 5

Resist the temptation to condemn the catalytic converter if higher than normal temperature readings are observed, since excessive temperatures are often caused by restrictions in the exhaust system. Check this as follows, but wait for the exhaust system to cool down to avoid burns and scalds-

  • Remove the upstream oxygen or air/fuel ratio sensor, and screw the pressure gauge into the exhaust system in its place. Start the engine and allow it to idle while you are observing the exhaust backpressure. Note the pressure reading, and compare this value with the maximum allowable value stated in the manual. Note that this value varies greatly between applications; therefore, there is no single value that is valid for all applications. If the actual backpressure exceeds the maximum allowable value, there is a restriction in either in the converter, or somewhere else in the exhaust system.
  • To narrow down the location of the restriction, refit the upstream sensor, and screw the pressure gauge into the exhaust system in the place of the downstream sensor, and take a pressure reading with the engine idling. If the measured backpressure remains the same, the restriction is in one or more mufflers: however, if the backpressure now falls into the acceptable range as specified by the manual, the restriction is in the catalytic converter.

NOTE: Step 5 assumes that there are no leaks in the exhaust system. If exhaust leaks are present, repair them to industry standards before repeating the backpressure test to avoid a misdiagnosis.

Step 6

If no excessive catalytic converter temperatures are found and the exhaust backpressure falls within acceptable limits, it is almost certain that the converter has failed due to long use. This can be confirmed by the fact that its temperature remains below 400 deg F (200 deg C) even after expended periods of driving.

As stated elsewhere in this guide, replacing a catalytic converter almost always requires equipment and skills that most non-professional mechanics do not possess or have access to. Thus, if a defective catalytic converter is diagnosed, the better option is to refer the vehicle to a specialist exhaust fitment shop for professional assistance.

Codes Related to P0432

  • P0430 – “Catalyst System Efficiency Below Threshold (Bank 2)”
  • P0431 – “Warm Up Catalyst Efficiency Below Threshold (Bank 2)”
  • P0433 – “Heated Catalyst Efficiency Below Threshold (Bank 2)”
  • P0434 – “Heated Catalyst Temperature Below Threshold (Bank 2)”

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