What does it mean when the car engine yellow light is on?

[Lucas]

The reasons for the car engine yellow light being on: 1. Sensor issues: including water temperature, crankshaft position, air flow, intake temperature, oxygen sensors, etc. When these sensors are damaged, have poor contact, or signal interruption, the car's ECU cannot accurately obtain engine data, which will trigger the engine fault light. 2. Maintenance issues: Poor engine maintenance is a cause of the engine fault yellow light. 3. Fuel and oil quality issues: The fuel added to cars usually has a specific grade, and engine oil can be semi-synthetic or fully synthetic. Manufacturers generally recommend which grade of fuel and type of oil to use. Failure to follow these recommendations over time can cause engine wear, triggering the fault light. 4. Poor combustion of the air-fuel mixture: Issues such as faulty spark plugs, ignition coils, fuel pump, or clogged fuel lines can all cause poor combustion of the engine's air-fuel mixture.