Warm Up Catalyst Efficiency Below Threshold (Bank 2)
What does P0431 mean?
The P0431 code means the vehicle's onboard diagnostic system has detected: Warm Up Catalyst Efficiency Below Threshold (Bank 2). This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Sulfur or rotten egg smell from exhaust
- Slightly reduced fuel economy
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Deteriorated warm-up catalytic converter on Bank 2 Very High
- Engine misfire on Bank 2 cylinders damaging the catalyst High
- Exhaust leak before the Bank 2 downstream O2 sensor Moderate
- Faulty Bank 2 downstream oxygen sensor Low
Step-by-Step Diagnostic Procedure
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Compare Bank 2 upstream and downstream O2 sensor waveforms -- downstream should be steady if the cat is healthy
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Check for misfires on Bank 2 cylinders that could damage the catalyst
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Inspect for exhaust leaks on the Bank 2 exhaust manifold and piping
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Monitor catalyst temperature with an infrared thermometer -- outlet should be hotter than inlet
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Replace the warm-up catalyst on Bank 2 if all other checks pass
Frequently Asked Questions
Can I drive with code P0431?
Yes. The vehicle drives normally. Bank 2 warm-up catalyst efficiency is reduced, increasing emissions. You will fail an emissions test but engine performance is not affected.
What is Bank 2?
Bank 2 is the side of the engine that does not contain cylinder 1. On V6 and V8 engines, each bank has its own catalytic converter and oxygen sensors.
Should I replace both Bank 1 and Bank 2 catalysts at the same time?
Not necessarily. If only Bank 2 has failed, you can replace just that converter. However, if both are close in age and mileage, replacing both prevents a return visit when the other side fails.