Summary
P0430 is the Bank 2 version of P0420 — the catalytic converter on the opposite side of a V-engine is not reducing emissions efficiently enough. The most common cause is a failing catalytic converter (45%), followed by a faulty downstream O2 sensor on Bank 2 (25%) and exhaust leaks (15%). If you also have P0420, both converters or a shared upstream problem needs attention. Start with the Bank 2 O2 sensor ($25–$120) before condemning the converter.
Severity: Moderate — not immediately dangerous
Safe to drive: Yes, with caution — emissions increase, fuel economy drops
Repair cost: $25–$2,500 depending on cause
DIY difficulty: Moderate to Advanced
What does P0430 mean?
P0430 is identical in meaning to P0420, but for Bank 2. The PCM compares the upstream (pre-cat) and downstream (post-cat) O2 sensors on Bank 2. When the downstream sensor begins mirroring the upstream sensor's oscillation pattern, the PCM determines the catalytic converter on that bank has lost efficiency and sets P0430.
Bank 2 is the side of the engine that does not contain cylinder 1. On V6 and V8 engines, this is typically the passenger side (but check your service manual — it varies by manufacturer). On inline 4-cylinder and inline 6-cylinder engines, there's only one bank, so you won't see P0430 on those — only P0420.
If you have both P0420 and P0430 at the same time, the problem may be upstream of both converters — a rich-running condition, misfires, or contamination affecting both banks.