What Causes the Engine Warning Light to Illuminate and the Car to Fail to Start?
2 Answers
Engine warning light illumination and failure to start could be caused by substandard fuel quality, oxygen sensor malfunction, mass air flow sensor failure, spark plug carbon buildup, or engine knocking. Below are the reasons for the engine warning light illuminating and the car failing to start: 1. Poor fuel quality, not meeting standards: Shortly after refueling, the engine warning light on the dashboard illuminates. This is usually due to filling up with low-quality fuel at non-standard gas stations, leading to incomplete combustion of the air-fuel mixture during engine operation and triggering the engine warning light. This does not affect driving safety but may harm the engine to some extent. 2. Oxygen sensor malfunction: Modern cars are equipped with two oxygen sensors, one before and one after the catalytic converter. The front oxygen sensor detects the air-fuel ratio under different engine conditions, while the ECU uses this signal to adjust fuel injection and calculate ignition timing. The rear sensor primarily monitors the performance of the catalytic converter. Therefore, if the oxygen sensor is damaged or its connector is faulty or loose, it can cause the air-fuel mixture to be too lean or too rich, triggering the warning light. 3. Mass air flow sensor malfunction: The mass air flow sensor, also known as the air flow meter, measures the amount of air intake and converts it into an electrical signal sent to the ECU. Based on the optimal air-fuel ratio, the ECU determines the amount of fuel to inject. If the mass air flow sensor or its circuit fails, the ECU will not receive the correct air intake signal, leading to improper fuel control and resulting in a mixture that is too lean or too rich, causing the engine to malfunction. 4. Spark plug carbon buildup: The varying quality of fuel on the market and congested urban traffic make it easy for spark plugs to accumulate carbon deposits. Carbon buildup on spark plugs can lead to poor engine performance, including difficulty starting, unstable idling, poor acceleration, backfiring during sudden acceleration, excessive exhaust emissions, and increased fuel consumption. 5. Engine knocking: When the engine draws in the air-fuel mixture, factors beyond control cause the mixture to ignite prematurely before reaching the intended ignition point during the compression stroke. The resulting shockwave opposes the piston's movement, causing engine vibration, a phenomenon known as knocking. Symptoms include reduced power, excessive engine noise, and, in severe cases, knocking sounds from the cylinders.
Having driven for over 30 years, I've encountered quite a few situations where the engine malfunction light comes on and the car won't start. A dead battery is the most common cause, especially in winter or after prolonged periods of inactivity—aging batteries or leaving lights on can both lead to insufficient voltage. Next is starter motor issues, such as worn carbon brushes or burnt-out coils, where turning the key only produces a clicking sound without the engine responding. Fuel system failures are another culprit, like a broken fuel pump cutting off supply, clogged fuel injectors, or faulty ignition coils preventing spark plugs from firing. Sensor malfunctions shouldn't be overlooked either—a failed crankshaft position sensor can prevent the ECU from controlling ignition timing. You can check the battery with jumper cables, listen for the fuel pump's humming sound, but the key is using an OBD scanner to read trouble codes. Never force-start the engine in these scenarios to avoid further damage.
