What does P0430 catalyst efficiency below threshold bank 2 mean?
Short answer: The engine computer compared the upstream and downstream oxygen sensors on bank 2 and decided the catalytic converter is not storing oxygen as well as it should; the converter may be worn, but sensors, leaks or engine problems can cause it too.
A healthy catalytic converter smooths out the oxygen content of the exhaust, so the downstream sensor shows a fairly steady signal while the upstream sensor switches. When the downstream signal starts to mirror the upstream sensor, the computer concludes the converter has lost efficiency.
Before condemning the converter, rule out exhaust leaks near the sensors, a lazy or contaminated downstream sensor, misfires, and fuel trim problems. A misfire or rich condition can damage a converter, and a new converter will fail again if the cause is not fixed.
Check Mode 6 catalyst test results if available, compare the two banks if the engine has P0420 and P0430 monitors, and review oxygen sensor data at a steady cruise. Check bulletins, since some vehicles have software updates for catalyst monitoring. Let the exhaust cool before inspecting it, because converters run extremely hot.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.