Aged or degraded heated catalytic converter on bank 2 that has lost oxygen-storage capacity; A faulty downstream oxygen sensor on bank 2 providing inaccurate readings to the PCM; Exhaust leaks upstream of the catalytic converter or near the sensor bungs, allowing outside air to skew readings; Engine misfires or rich fuel mixtures that have overheated or contaminated the catalyst over time; Oil or coolant consumption entering the exhaust stream and poisoning the catalyst; Wiring or connector issues at the bank 2 downstream oxygen sensor or its heater circuit; A failing bank 2 upstream oxygen sensor causing incorrect fuel control and catalyst damage

DTC codes / P04xx · Auxiliary emission controls / P0433

P0433Heated Catalyst Efficiency Below Threshold (Bank 2)

Q: What does code P0433 mean?

Heated Catalyst Efficiency Below Threshold (Bank 2). P0433 means the powertrain control module (PCM) has determined that the bank 2 heated catalytic converter is not cleaning the exhaust as efficiently as it should, based on oxygen sensor readings before and after the converter. The PCM compares the switching activity of the downstream oxygen sensor to the upstream sensor and sets this code when the catalyst's oxygen-storage capacity falls below the expected threshold.

P0433 means the powertrain control module (PCM) has determined that the bank 2 heated catalytic converter is not cleaning the exhaust as efficiently as it should, based on oxygen sensor readings before and after the converter. The PCM compares the switching activity of the downstream oxygen sensor to the upstream sensor and sets this code when the catalyst's oxygen-storage capacity falls below the expected threshold.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other symptoms noticed by the driver
A slight decrease in fuel economy as the PCM may adjust fuel trim to compensate
Occasional rough idle or hesitation during acceleration if the catalyst is severely degraded
A faint sulfur or rotten-egg smell from the exhaust in some cases
Failed emissions inspection due to increased hydrocarbon (HC) emissions
In rare cases, a noticeable loss of power if the catalyst is partially clogged

Common causes, most likely first

Aged or degraded heated catalytic converter on bank 2 that has lost oxygen-storage capacity
A faulty downstream oxygen sensor on bank 2 providing inaccurate readings to the PCM
Exhaust leaks upstream of the catalytic converter or near the sensor bungs, allowing outside air to skew readings
Engine misfires or rich fuel mixtures that have overheated or contaminated the catalyst over time
Oil or coolant consumption entering the exhaust stream and poisoning the catalyst
Wiring or connector issues at the bank 2 downstream oxygen sensor or its heater circuit
A failing bank 2 upstream oxygen sensor causing incorrect fuel control and catalyst damage

How to diagnose and fix it

Use a scan tool to verify the code and check for any related misfire, fuel trim, or oxygen sensor codes that could be the root cause
Inspect the bank 2 exhaust system for leaks, loose clamps, and damaged gaskets, and repair any leaks before condemning the converter
Graph the bank 2 upstream and downstream oxygen sensor signals to confirm the downstream sensor is switching similarly to the upstream sensor, indicating a degraded catalyst
Test the bank 2 downstream oxygen sensor and its heater circuit for proper operation, and replace the sensor if it is sluggish or unresponsive
Check for engine misfires, fuel system issues, or oil/coolant consumption that could have damaged the catalyst, and repair those faults first
If the catalyst is confirmed degraded after all other causes are ruled out, replace the bank 2 heated catalytic converter with a quality unit
Clear the codes and perform a drive cycle to verify the repair and ensure the monitor completes without resetting the code

Before you replace the bank 2 converter

A lazy downstream oxygen sensor can mimic a failed catalyst, so always compare its switching activity to the upstream sensor before condemning the converter.
Exhaust leaks between the engine and the downstream sensor can pull in outside air and cause the PCM to see false lean readings, setting P0433 even when the catalyst is healthy.
An underlying misfire or rich condition that overheated the catalyst will quickly destroy a new converter, so those faults must be fixed first.
On some vehicles, a weak battery or charging system issue can cause erratic sensor readings and false catalyst codes, so check system voltage as part of diagnosis.
The code does not always mean the converter is completely failed; it indicates efficiency has dropped below a threshold, and in some cases a good Italian tune-up (high-speed driving) can temporarily improve catalyst performance.

Can I keep driving with P0433?

You can generally continue driving with P0433, but avoid aggressive acceleration and heavy loads until the fault is diagnosed, as a failing catalyst can worsen and lead to higher emissions or reduced performance. Have the vehicle inspected soon to prevent potential damage to other components and to ensure it passes emissions testing.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.