What does it mean when the yellow engine light comes on?

[CatherineMarie]

Here are the reasons why the engine indicator light turns yellow: 1. Poor quality gasoline that does not meet standards. Poor quality gasoline not only leads to incomplete combustion of the air-fuel mixture in the cylinders, resulting in excessive carbon deposits, but also poses risks of clogging fuel lines and corroding components. 2. Oxygen sensor failure. Typically, there are two oxygen sensors installed in a car, one before and one after the three-way catalytic converter. The front oxygen sensor detects the air-fuel ratio under different engine operating conditions, while the ECU adjusts the fuel injection amount and calculates ignition timing based on this signal. The rear sensor primarily monitors the performance of the three-way catalytic converter. 3. Airflow sensor failure. The air flow meter converts the detected intake air volume into an electrical signal and sends it to the engine computer, which then determines the fuel amount based on the optimal air-fuel ratio. 4. Spark plug carbon deposits. Carbon buildup on spark plugs can cause poor engine performance, leading to difficulties in starting, unstable idling, poor acceleration, backfiring during sudden acceleration, excessive exhaust emissions, increased fuel consumption, and other abnormal symptoms. 5. Engine knocking. Knocking can be categorized as noticeable or unnoticeable. In the case of unnoticeable knocking, the engine computer adjusts the ignition timing advance/retard based on signals from the knock sensor to minimize knocking. However, when unnoticeable knocking exceeds the adjustable range of the engine computer, the engine warning light will also illuminate. 6. Coolant temperature sensor failure. Inside the coolant temperature sensor is a thermistor, which has higher resistance at lower temperatures and lower resistance at higher temperatures. When the engine coolant is cold, the temperature information sent by the coolant temperature sensor to the ECU enriches the air-fuel mixture to stabilize engine operation. 7. Engine misfire. A misfiring engine can result in high fuel consumption, black smoke, poor acceleration, severe vibration, increased engine noise, and a higher likelihood of stalling. Misfires are mainly caused by issues in the ignition system and fuel supply system, including carbon deposits on spark plugs and damage to the high-pressure fuel pump.