P0430 Catalyst System Efficiency Below Threshold (Bank 2)
Same diagnosis as P0420 but for Bank 2 of a V-engine. Bank 2 is the side of the engine that does NOT contain cylinder #1.
Definition
P0430 is the Bank 2 equivalent of P0420. The diagnosis path is identical, but applied to the opposite cylinder bank. On V6 and V8 engines, Bank 2 is the side of the engine that does NOT contain cylinder #1; cylinder numbering varies by manufacturer so confirm against the service manual before condemning a part.
Common causes
- Failed or degraded catalytic converter (Bank 2)
- Failed downstream (post-cat) oxygen sensor on Bank 2
- Exhaust leak upstream of the Bank 2 post-cat O2 sensor
- Engine running rich or lean on Bank 2
- Damaged catalyst substrate from misfires on Bank 2
Common misdiagnoses
- Treating P0430 as identical to P0420 without confirming which physical bank is Bank 2 on the engine.
- Replacing Bank 1 components when Bank 2 is the affected side.
Troubleshooting steps
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1. Identify Bank 2
Consult the service manual or VIN-specific reference to confirm which side of the engine is Bank 2.
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2. Follow the P0420 diagnostic procedure
Apply the same steps as P0420 but to Bank 2 sensors and catalyst.