What Causes the Engine Warning Light with an Exclamation Mark?

[DeBrynlee]

There are 7 main reasons why the engine warning light may illuminate: Sensor Malfunction: This includes sensors such as coolant temperature, crankshaft position, air flow, intake air temperature, and oxygen sensors. When these sensors are damaged, have poor connections, or their signals are interrupted, the vehicle's ECU cannot accurately obtain engine data, which triggers the engine warning light. Fuel or Oil Quality Issues: If fuel or engine oil is not added according to the manufacturer's specifications, it may cause engine wear and trigger the warning light. Poor Combustion of 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 warning light will illuminate as a warning. Issues such as faulty spark plugs, ignition coils, fuel pumps, or clogged fuel lines can cause poor combustion. Turbocharger Problems: Issues with the intake boost piping or turbocharger can also trigger the engine warning light. The most common problem is turbocharger damage, which may also be accompanied by symptoms such as oil leaks, excessive oil consumption, reduced power, metallic noises, or blue/black smoke from the exhaust. Intake Problems: If the vehicle's intake system malfunctions, it may lead to blocked engine pipes, and in severe cases, trigger the engine warning light. A dirty air filter that is not cleaned regularly can cause intake issues. Exhaust Problems: Exhaust system faults can also cause the engine warning light to illuminate. Common causes include faulty rear oxygen sensors, catalytic converters, exhaust camshafts, or bearings, with the catalytic converter being the most frequent issue. Using leaded gasoline, lead- or silicon-containing lubricant additives, physical damage to the catalytic converter, or fuel system malfunctions can all lead to catalytic converter failure. Anti-Theft System Malfunction: If the vehicle's electronic anti-theft system fails or if the anti-theft controller does not match the engine's electronic controller, the anti-theft system may prevent the engine from operating normally and trigger the warning light. If the engine warning light illuminates, follow these steps: First, check whether the engine is running normally. If there are issues such as shaking or smoke, 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 and wait 5-10 minutes. Without pressing the brake pedal, press the start button once or turn the key halfway to the "ON" position (without pressing the clutch). The vehicle will perform a self-check after powering on. Observe whether the warning light turns off after 5-10 seconds. If the warning light remains on, visit a service center as soon as possible. Technicians can use a portable diagnostic tool to read the trouble codes, identify the issue, and perform targeted repairs.

[CamilleLee]

I've been driving for over a decade, and the most common cause of the engine warning light with an exclamation mark is sensor issues, such as an oxygen sensor clogged with carbon deposits or a crankshaft position sensor wiring harness chewed through by rodents. Last time a friend's car had the light on, it turned out to be poor fuel quality causing a clogged catalytic converter, which triggered the fault due to restricted exhaust flow. Dirty throttle bodies and aging ignition coils can also trigger warnings. When this light comes on, don't delay—get to a repair shop as soon as possible to read the fault codes with a diagnostic tool. If the light comes on while on the highway, maintain steady throttle, slow down gradually, and avoid shutting off the engine abruptly. Pull over at the nearest service area. Remember to turn off the air conditioning before shutting down the engine to prevent voltage issues during startup.