What Causes the System Malfunction Warning Light to Illuminate?
2 Answers
Reasons for the system malfunction warning light illuminating: 1. Sensor malfunction: To maintain the optimal air-fuel ratio of the combustible mixture, the ECU monitors the oxygen concentration in the exhaust via the oxygen sensor and adjusts the fuel injection accordingly. If the oxygen sensor fails, the ECU cannot receive the oxygen concentration signal, causing the engine malfunction indicator light to illuminate. 2. Engine knocking: Using gasoline with a lower octane rating than specified, engine overheating, or severe carbon buildup in the combustion chamber can lead to engine knocking. Although the ECU can detect knocking through the knock sensor and mitigate it by delaying ignition timing, if the knocking exceeds the ECU's processing capacity, the engine malfunction indicator light will illuminate due to engine knocking. 3. Mass airflow sensor malfunction: The engine also measures the intake air volume via the mass airflow sensor to control the air-fuel ratio and adjust fuel injection. If the mass airflow sensor malfunctions and the ECU cannot receive the air flow signal, the engine malfunction indicator light will also illuminate.
I've seen many cases like this. The system malfunction warning light comes on, usually the engine fault light, the yellow one. The most common reason is a faulty O2 sensor, which monitors exhaust oxygen levels and triggers an alarm when it ages. Alternatively, there might be an issue with the ignition system, such as carbon buildup on the spark plugs causing unstable ignition. It could also be a bug in the computer control module, like a software false alarm or a loose wiring harness. Last time my car's light came on, the check revealed the gas cap wasn't tightened properly, causing a leak that triggered the sensor. If the ABS light is on, it might be due to a dirty brake wheel speed sensor; the airbag light often indicates aging circuits. In short, don't take it lightly—find a safe place to stop and check immediately, or go to a repair shop to read the fault codes with a computer. Delaying could lead to engine damage or safety risks.
