Reasons for the Engine Warning Light Illuminating in Yellow

[LaKennedy]

Below are the reasons why the engine warning light illuminates in yellow: 1. Poor-quality gasoline that does not meet standards. Low-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 such as clogging the fuel system and corroding components. 2. Oxygen sensor malfunction. Typically, a vehicle is equipped with two oxygen sensors, one before and one after the three-way catalytic converter. The front oxygen sensor detects the air-fuel ratio under different engine conditions, while the ECU adjusts the fuel injection quantity and calculates the ignition timing based on this signal. The rear sensor primarily monitors the performance of the three-way catalytic converter. 3. Faulty air flow sensor. The air flow meter converts the detected intake air volume into an electrical signal and sends it to the engine control unit (ECU), which then determines the optimal air-fuel ratio and indirectly controls the fuel quantity. 4. Spark plug carbon deposits. Carbon buildup on spark plugs can cause poor engine performance, leading to issues such as difficulty starting, unstable idling, poor acceleration, backfiring during rapid acceleration, excessive exhaust emissions, increased fuel consumption, and other abnormal symptoms. 5. Engine knocking. Knocking can be categorized as noticeable or unnoticeable. In cases of unnoticeable knocking, the engine ECU adjusts the ignition timing advance or retard based on signals from the knock sensor to minimize knocking. However, when the unnoticeable knocking exceeds the ECU's adjustable range, the engine warning light will illuminate as an alert. 6. Damaged coolant temperature sensor. Inside the coolant temperature sensor is a thermistor, whose resistance increases with lower temperatures and decreases with higher temperatures. When the engine coolant is cold, the sensor sends a signal to the ECU, enriching the air-fuel mixture to stabilize engine operation. 7. Engine misfire. Misfiring can result in symptoms such as increased fuel consumption, black smoke emissions, poor acceleration, severe vibration, louder engine noise, and a higher likelihood of stalling. Misfires are primarily caused by issues in the ignition system or fuel supply system, including carbon deposits on spark plugs or a faulty high-pressure fuel pump.