What are the reasons for the engine malfunction indicator light to illuminate?
2 Answers
The engine malfunction indicator light may illuminate due to the following 7 main reasons: Sensor malfunction: The sensors referred to here include coolant temperature, crankshaft position, air flow, intake air temperature, oxygen sensors, etc. When these sensors are damaged, have poor connections, or experience signal interruptions, the vehicle's ECU cannot accurately obtain engine data, which will trigger the engine malfunction indicator light. Fuel quality issues: If fuel and engine oil are not added according to the manufacturer's requirements, it may cause engine wear and trigger the malfunction light. Poor combustion of the air-fuel mixture: Poor combustion can lead to engine carbon buildup or knocking. When detected by the oxygen sensor and reported to the ECU, the malfunction light will illuminate as a warning. Issues such as spark plug failure, ignition coil failure, fuel pump failure, or fuel line blockage can all cause poor combustion of the air-fuel mixture. Turbocharging problems: The intake turbocharging pipeline and turbocharger can also cause the engine malfunction light to illuminate. The most common issue is turbocharger damage, accompanied by symptoms such as oil leaks, excessive oil consumption, reduced power, metallic noises, or blue/black smoke from the exhaust. Intake problems: If there is an issue with the vehicle's intake, it may lead to engine pipeline blockage, and in severe cases, trigger the engine malfunction light. A dirty air filter that is not cleaned regularly can cause intake problems. Exhaust problems: Exhaust system faults can also trigger the engine malfunction light. Issues such as rear oxygen sensor failure, catalytic converter failure, exhaust camshaft and bearing failure can all cause exhaust problems, with the catalytic converter being the most common. Using leaded gasoline, lead or silicon-based lubricant additives, physical damage to the catalytic converter, or fuel system malfunctions can easily lead to catalytic converter failure. Anti-theft system malfunction: If the vehicle's electronic anti-theft system malfunctions, or if the anti-theft controller does not match the engine electronic controller, the anti-theft system can prevent the engine from operating normally and trigger the malfunction light. If the engine malfunction light illuminates, follow these steps: First, check if the engine is running normally, and if there are any issues such as shaking or black smoke. If so, avoid restarting the engine. Note: Do not restart the engine if the red warning light is on. If the engine can be started, turn it off for 5-10 minutes, then without pressing the brake, press the start button once or turn the key halfway to the 'on' position without depressing the clutch. The vehicle will perform a self-check after powering on. Wait for 5-10 seconds and observe if the malfunction light turns off. If the malfunction light remains on, visit a service station as soon as possible. The service station can use a portable diagnostic tool to read the fault codes, identify the issue, and perform targeted repairs.
I've been running an auto repair shop for over a decade and have seen plenty of instances where the engine warning light comes on. The cause usually lies with the sensors—for example, a faulty oxygen sensor can give incorrect exhaust readings. Or it could be a fuel system issue, like clogged fuel injectors causing the mixture to run too rich, making the car shake. Problems with the ignition system are also common, such as worn-out spark plugs or faulty ignition coils leading to incomplete combustion. Emission control components like a stuck EGR valve or a clogged catalytic converter can also trigger the light. Sometimes, low battery voltage or unstable alternator output can cause this issue too. I always advise car owners to start with simple checks—like making sure the fuel cap is tight (just screw it back on if loose). If that doesn't help, use an OBD scanner to read the trouble codes—for instance, P0420 indicates catalytic converter failure—and then fix accordingly. Never ignore it and keep driving, as it'll just increase fuel consumption and damage the engine, leading to higher maintenance costs.
