P0430: Catalyst System Efficiency Below Threshold (Bank 2)
Title: SAE J2012 generic definition. Manufacturer-specific definitions and enhanced codes can differ; check service information for the exact vehicle.
What P0430 means
Same catalyst test as P0420, failed by the bank 2 converter on a V or flat engine.
What sets it
The bank 2 catalyst monitor compares bank 2's upstream and downstream oxygen sensors. If bank 1 passes and bank 2 fails, you can compare the two banks on the same vehicle, which is a big diagnostic advantage.
Symptoms
- Usually none apart from the light
- Inspection failure
Is it safe to drive?
General guidance, not a guarantee: Usually OK short-term; fix any upstream cause promptly so it doesn't spread to the other converter. If in doubt, have it towed and diagnosed.
Common causes
Listed roughly from most to least common in general practice. The real order varies by vehicle, mileage and history.
- Bank 2-specific engine issue: misfire on a bank 2 cylinder, leaking injector on bank 2
- Worn bank 2 converter
- Exhaust leak on bank 2
- Bank 2 downstream sensor
Test before you replace: diagnostic sequence
General guidance only. Always follow the vehicle manufacturer's service information, specifications and safety procedures. Any figures below are general guidelines that defer to the manufacturer's specification.
- Repair misfire and fuel-trim codes first, paying attention to bank 2 cylinders.
- Graph bank 1 and bank 2 downstream sensors side by side under the same conditions. The healthy bank is your reference for comparison.
- Check bank 2 exhaust for leaks near its sensors.
- Review Mode $06 catalyst results for both banks.
- Replace only with a legal converter for that vehicle and state, after the root cause is fixed.
- Run a drive cycle and confirm the monitor passes.
Bench note: Comparing the two banks on the same vehicle is better than any generic waveform example.
Related codes
FAQ
Does P0430 mean both converters are bad?
No. It refers to bank 2 only. If P0420 isn't set, bank 1 passed its test.
Where is bank 2?
On the side of the engine opposite cylinder 1. Check the service information for your engine.
Sources
- SAE J2012, Diagnostic Trouble Code Definitions (standard page; code titles only)
- California Code of Regulations, 13 CCR 1968.2, OBD II requirements (via Cornell LII)
- SAE J1979, E/E Diagnostic Test Modes (Mode $06, readiness, freeze frame)
- US EPA, Enforcement discretion for California-approved aftermarket catalytic converters
- US EPA, Tampering Policy (2020), incl. note on the 1986 aftermarket catalyst policy
Written with AI assistance and reviewed for accuracy; not a substitute for OEM service information. Shop Docs Studio is not affiliated with SAE, EPA, CARB or any vehicle manufacturer.