P0430: Catalyst System Efficiency Below Threshold (Bank 2)
P0430 is the Bank 2 counterpart of P0420. On a V6, V8 or flat engine, Bank 2 is the cylinder bank that does not contain cylinder number one. The code means the converter serving that bank is no longer buffering oxygen the way the engine computer expects.
Can I still drive with P0430?
Yes, in most cases
Same as P0420: not a safety fault by itself, but an emissions failure. Stop driving if you hear rattling from the exhaust or lose noticeable power.
What you will actually notice
- Check engine light with no obvious change in driving
- Failed emissions test
- Occasional sulphur smell from the exhaust
- Sometimes set together with P0420 when both converters are aged
Causes, ordered by how often they turn out to be the fault
1.Bank 2 catalytic converter worn out
Very commonTypically age-related on higher-mileage V-configuration engines.
2.Slow downstream oxygen sensor on Bank 2
CommonTest before replacing, exactly as with P0420.
3.Exhaust leak on the Bank 2 side
CommonManifolds and flex pipes on the rear bank are common leak points.
4.Aftermarket converter below OEM specification
CommonSame trap as P0420.
5.Rich running or oil consumption on that bank
Less commonCheck for bank-specific fuel trim codes.
How to diagnose it, cheapest test first
Work down this list in order. The most expensive mistake with this code is replacing a costly part before ruling out a cheap one.
- 1
Confirm which bank is Bank 2 for your specific engine
FreeGetting this backwards means replacing the wrong converter. Bank 2 does not contain cylinder 1.
- 2
Read all codes and freeze frame data
Free at most parts storesAddress any misfire or fuel trim codes on that bank first.
- 3
Inspect the Bank 2 exhaust path for leaks
Free to inspectRear-bank manifolds are awkward to reach and frequently crack.
- 4
Compare sensor waveforms on Bank 2
LowRear sensor should be far steadier than the front one.
- 5
Replace the Bank 2 downstream sensor if proven slow
ModerateRear-bank sensors are often harder to access, which raises labour.
- 6
Replace the Bank 2 catalytic converter
HighOnly after the cheaper causes are eliminated.
What the repairs typically cost
| Repair | Estimated range |
|---|---|
| Bank 2 downstream oxygen sensor replacementOften costs more than Bank 1 purely because of access. | $180 – $450 |
| Exhaust leak repairRear-bank manifold work is labour-heavy on many V engines. | $100 – $600 |
| Catalytic converter replacementIf both banks are aged, doing them together saves on labour. | $500 – $2,500 |
Estimate only. Ranges vary widely by region, vehicle and shop rate, and are not quotes. Always get a written estimate before authorising work.
Notes for specific makes
Ford
On several V6 engines the rear manifold cracks and mimics a converter failure. Inspect it before spending on a converter.
Nissan / Infiniti
Bank identification is a frequent source of misdiagnosis on VQ engines. Verify against the service manual.
Subaru
On flat engines, bank layout is not intuitive. Confirm before ordering parts.
Common questions
Which side is Bank 2?
Bank 2 is the cylinder bank that does not contain cylinder number one. Which physical side that is depends entirely on the engine, so check your service data rather than guessing.
I have both P0420 and P0430. Do I need two converters?
Not necessarily. Both codes appearing together often points at a shared cause such as an engine running rich, so diagnose the engine before buying two converters.
Is P0430 more serious than P0420?
No. They are the same fault on different banks and carry the same urgency.
Not sure which of these applies to your car?
Describe what the car is actually doing and get a diagnosis narrowed to your vehicle, or find a shop near you.
AI-generated and informational only. This is not a diagnosis of your specific vehicle and does not replace inspection by a qualified technician.