System: Emissions Control · Standard: SAE J2012 generic code · Severity: Low urgency
No immediate safety risk. Monitor it and fix it at the next service, but do not ignore it indefinitely.
Never replace the converter on this code alone. A misfire, a rich condition or a lazy oxygen sensor will destroy a new converter within weeks. Fix the cause first.
Start by reading every stored and pending code, not just this one. A single fault frequently sets three or four codes at once, and the first one in the freeze-frame data is usually the cause while the rest are consequences.
The downstream oxygen sensor shows the catalytic converter is not storing and releasing oxygen as it should. Catalyst System Efficiency Below Threshold (Bank 1) is a generic emissions control code defined by SAE J2012, so it carries the same meaning on every OBD-II vehicle.
Low urgency. No immediate safety risk. Monitor it and fix it at the next service, but do not ignore it indefinitely.
In rough order of how often they turn out to be the problem: Ageing catalytic converter; Failed downstream oxygen sensor; Exhaust leak before the converter.
P0401 Exhaust Gas Recirculation Flow InsufficientP0402 Exhaust Gas Recirculation Flow ExcessiveP0411 Secondary Air Injection System Incorrect FlowP0430 Catalyst System Efficiency Below Threshold (Bank 2)P0440 Evaporative Emission Control System MalfunctionP0442 Evaporative Emission Control System Leak Detected (Small Leak)Code number, system and definition follow the SAE J2012 / ISO 15031-6 generic diagnostic trouble code standard. Symptoms, causes and severity are the standard generic diagnostic logic for that fault. This page does not contain manufacturer-specific procedures, part numbers or pricing.