What are the reasons for the engine warning light to illuminate in a Passat?

[ODaniella]

The engine warning light may illuminate due to the following 7 main reasons: Sensor malfunction: This includes sensors such as coolant temperature, crankshaft position, air flow, intake temperature, and oxygen sensors. When these sensors are damaged, have poor contact, or experience signal interruption, the vehicle's ECU cannot accurately obtain engine data, triggering the warning light. Fuel/oil quality issues: Failure to use fuel and engine oil as specified by the manufacturer may cause engine wear, leading to illumination of the warning light. Poor fuel mixture combustion: This can cause engine carbon buildup or knocking. When detected by oxygen sensors and reported to the ECU, the warning light activates. Common causes include spark plug failure, ignition coil issues, fuel pump malfunction, or fuel line blockage. Turbocharger problems: Issues with intake boost pipes or turbocharger can trigger the warning light. The most common symptom is turbocharger damage, accompanied by oil leaks, excessive oil consumption, power loss, metallic noises, or blue/black exhaust smoke. Intake system issues: Air intake problems may lead to engine pipe blockage, potentially triggering the warning light. A dirty air filter that hasn't been regularly cleaned is a common cause. Exhaust system problems: Exhaust faults can activate the warning light. Common causes include rear oxygen sensor failure, catalytic converter issues (most frequent), or exhaust camshaft/bearing problems. Using leaded gasoline, lead/silicon-containing lubricant additives, physical damage to the catalytic converter, or fuel system malfunctions may cause catalytic converter failure. Anti-theft system malfunction: If the electronic anti-theft system fails or doesn't match with the engine control unit, it may prevent normal engine operation while illuminating the warning light. When the engine warning light illuminates, follow these steps: First check if the engine operates normally. If there's shaking, black smoke, etc., avoid restarting. Never restart if the red warning light is on. If the engine can start, turn off for 5-10 minutes, then without pressing brakes, push the start button (or turn the key halfway to ON position without depressing clutch). The vehicle will perform self-diagnosis for 5-10 seconds - observe if the warning light turns off. If the light remains on, visit a service center immediately. Technicians can use diagnostic tools to read trouble codes and perform targeted repairs.