P0431: Warm Up Catalyst Efficiency Below Threshold (Bank 2)

What Does P0431 Mean?

Code P0431 indicates that the warm-up catalytic converter on bank 2 is not operating efficiently enough during the warm-up period. This is the bank 2 counterpart to P0421 and applies to engines with two cylinder banks, such as V6 or V8 configurations. The downstream oxygen sensor on bank 2 shows the converter is underperforming.

Common Causes

• Worn warm-up catalytic converter on bank 2
• Faulty downstream oxygen sensor on bank 2
• Exhaust leak on bank 2 before the converter
• Rich fuel condition on bank 2
• Oil or coolant contamination of the catalyst

Symptoms

• Check engine light on
• Failed emissions test
• Slight decrease in fuel economy
• Possible sulfur smell from exhaust

Diagnostic Steps

1. 1Retrieve freeze frame data and check for bank 2 specific faults
2. 2Monitor bank 2 upstream and downstream O2 sensor waveforms
3. 3Inspect bank 2 exhaust for leaks at the manifold and connections
4. 4Check for engine misfires on bank 2 cylinders that could damage the converter
5. 5Verify bank 2 fuel trim values are within normal range
6. 6Test downstream O2 sensor on bank 2 for proper response

Estimated Repair Cost

Frequently Asked Questions