What are the reasons for the engine warning light in Ford Focus?

[AveryAnn]

The engine warning light in Focus may illuminate due to the following 7 main reasons: Sensor malfunction: The sensors mentioned here include coolant temperature, crankshaft position, air flow, intake air temperature, oxygen sensors, etc. When these sensors are damaged, have poor contact, or signal interruption, the vehicle's ECU cannot accurately obtain engine data, which will trigger the engine warning light. Fuel/oil quality issues: If fuel and engine oil are not added according to the manufacturer's requirements, it may cause engine wear and trigger the warning light. Poor mixture combustion: Poor combustion can lead to engine carbon deposits or knocking. When detected by oxygen sensors and reported to the ECU, the warning light will illuminate as an alert. Spark plug failure, ignition coil failure, fuel pump failure, or fuel line blockage can all cause poor mixture combustion. Turbocharging issues: Intake turbocharging pipelines or turbochargers can also trigger the engine warning light. The most common is turbocharger damage, accompanied by symptoms like oil leaks, excessive oil consumption, power loss, metallic noises, or blue/black smoke from the exhaust. Intake issues: Problems with the car's intake system may cause engine pipeline blockages, and severe cases will trigger the warning light. A dirty air filter that isn't cleaned regularly can lead to intake problems. Exhaust issues: Exhaust faults can also cause the engine warning light to illuminate. Rear oxygen sensor, catalytic converter, exhaust camshaft, and bearing failures are common causes, with the catalytic converter being most frequent. Using leaded gasoline, lead/silicon-containing lubricant additives, physical damage to the catalytic converter, or fuel supply system failures can easily cause catalytic converter problems. Anti-theft system malfunction: If the electronic anti-theft system fails or the anti-theft controller doesn't match the engine ECU, the system 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. Particularly, never restart if the red warning light is on. If the engine can start, turn off for 5-10 minutes, then press the start button without braking, or turn the key halfway to ON position without depressing the clutch. The vehicle will initiate self-check upon power-on. Observe if the warning light turns off after 5-10 seconds. If the light persists, visit a service center promptly. Technicians can read fault codes via portable diagnostic tools to obtain specific failure information for targeted repairs.