Why is the yellow engine fault light on?

[GenesisFitz]

Engine fault light yellow light on reasons are as follows: 1. Oxygen sensor failure. If the oxygen sensor is damaged or the sensor plug is damaged or loose, it will cause the mixture to be too lean or too rich, thus triggering the fault light. 2. Substandard gasoline quality. Due to refueling with poor-quality gasoline at non-standard gas stations, the air-fuel mixture does not burn completely during engine operation. 3. Spark plug carbon deposits. Excessive carbon deposits can cause the ignition coil to reverse breakdown, leading to ignition coil failure, poor ignition, and incomplete combustion. Here is some extended information about the engine: 1. Fuel quality is the primary factor causing the engine fault light to illuminate. The anti-knock property of gasoline is represented by the octane number; the higher the octane number, the better the anti-knock property. 2. As regulations on engines become increasingly stringent, the quality indicators for fuel are also getting higher.