Why does the engine show a fault but can still start?

[VonJackson]

This situation is normal because not all engine faults affect driving. The engine light coming on is just a prompt that a certain component or part has a problem, unable to meet the engine's original standard requirements or driving conditions, hence the light indicates it's time for inspection and repair. Catalytic Converter: When the catalytic converter fails, it can lead to unqualified exhaust emissions. Another scenario is when the catalytic converter functions normally, but the exhaust emission data exceeds the specified standard values and cannot be corrected. Both situations can cause the engine fault light to illuminate. Oxygen Sensor: The oxygen sensor's role is to monitor the air-fuel ratio. If the air-fuel ratio of the mixture does not match the theoretical air-fuel ratio, the catalytic converter's effectiveness sharply declines. Therefore, if the oxygen sensor fails to detect the air-fuel ratio correctly, the engine's computer cannot obtain normal detection data nor adjust the air-fuel ratio, resulting in the engine fault light coming on.