What are the common causes of P0431?

A worn or contaminated catalytic converter on bank 2. A lazy upstream oxygen sensor on bank 2. An exhaust leak ahead of the bank 2 converter. A misfire or rich condition damaging the bank 2 converter. Oil or coolant burning through the bank 2 converter.

Compare upstream and downstream O2 sensor switching on bank 2. Check for exhaust leaks before and after the bank 2 converter. Check misfire counters and fuel trims on bank 2. Inspect the bank 2 converter for contamination or damage. Replace the bank 2 converter if efficiency stays low. Clear the code and retest.

P0431

Catalyst 1 Efficiency Below Threshold Bank 2

System: Auxiliary emission controls (P code)
Lamp: Check Engine Light
Category: Powertrain - Auxiliary Emissions Controls

What it means

P0431 means Catalyst 1 Efficiency Below Threshold Bank 2.

Check these first

A worn or contaminated catalytic converter on bank 2
A lazy upstream oxygen sensor on bank 2
An exhaust leak ahead of the bank 2 converter
A misfire or rich condition damaging the bank 2 converter
Oil or coolant burning through the bank 2 converter

What to do next

Compare upstream and downstream O2 sensor switching on bank 2
Check for exhaust leaks before and after the bank 2 converter
Check misfire counters and fuel trims on bank 2
Inspect the bank 2 converter for contamination or damage
Replace the bank 2 converter if efficiency stays low
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.