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P0420 Code: Catalyst System Efficiency Below Threshold — Causes, Symptoms & Fix P0420 means the catalytic converter on Bank 1 isn't cleaning exhaust efficiently enough. Learn the symptoms, r P0430 Code: Catalyst Efficiency Below Threshold (Bank 2) — Causes, Symptoms & Fix P0430 means bank 2's catalytic converter isn't cleaning exhaust efficiently — the same story as P0420, on the