P0430Catalyst System Efficiency Below Threshold (Bank 2)
Drive normally — check soon
What it means
The same fault as P0420, on the other bank: the downstream oxygen sensor behind bank 2's catalytic converter is seeing swings it should be smoothing out, so that converter is flagged as below efficiency. It applies to engines with two exhaust banks — V6s, V8s, and some flat and inline layouts with split exhaust.
Is it safe to drive?
Drive normally — check soon
Like P0420: the car drives normally, and nothing dramatic happens if you keep using it. It fails emissions testing until resolved, and any upstream cause — misfire, rich mixture, oil burning — should be fixed before a new converter goes in, or the new one dies the same death.
Common causes
Most likely first.
- A worn-out bank 2 catalytic converter — most likely with age and miles
- A lazy or failing downstream O2 sensor on bank 2
- An exhaust leak around the bank 2 sensors
- Misfires or rich running on bank 2 overheating the converter
- If P0420 is set too: a shared cause — oil or coolant burning, chronic rich running — worth finding before pricing two converters
What the live data shows
Bank 2 Sensor 2's voltage mirroring Bank 2 Sensor 1's oscillation is the signature, exactly as with P0420 on the other side. Comparing the two banks is the fast diagnosis: one bank clean and one mirroring localizes the fault; both banks mirroring suggests a shared root cause upstream. Bank 2 fuel trims help rule mixture problems in or out.
A scanner that reads all 139 standard sensors shows you these readings live. ScanMyCar charts them as you drive, keeps the freeze-frame stored with the code, and pulls codes from every module — free, with any cheap Bluetooth adapter.
Typical fixes
Cheapest first, where honesty allows.
- Check for exhaust leaks and inspect the bank 2 downstream sensor's wiring first
- Fix any bank 2 misfire or fuel-trim fault before condemning the converter
- Replace the downstream O2 sensor if its readings are implausible
- Replace the bank 2 catalytic converter with an OEM-grade unit
A guide, not a diagnosis. This page describes what P0430 generally means across OBD-II cars. What's actually wrong with your car depends on its live data and its history — and any repair decision deserves a proper diagnosis, whether that's you with a scanner or a professional with a lift.