Why is the engine warning light on in an Audi Q5?

[Eleanor]

The engine warning light can illuminate during power-on self-test or under other circumstances. The power-on self-test is an indicator that monitors the status of all vehicle sensors before driving. Generally, if the engine is not started after power-on, the light will turn off by itself after about 3 seconds. In other cases, if the EPC indicator light remains on after the vehicle is started, the main causes for the EPC light staying on include faults in the engine intake system, throttle valve issues, fuel system problems, engine malfunctions, ECU control unit failures, and brake light faults. Below is a detailed explanation of each type of fault: Sensor Issues: Sensors include those for coolant temperature, crankshaft position, air flow, intake temperature, oxygen levels, 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 warning light. Solution: If such issues occur, promptly visit a repair center for professional inspection to eliminate potential safety hazards. Maintenance Issues: Poor engine maintenance is the most common cause of the engine warning light turning on. Vehicles have specific maintenance cycles. If maintenance is not performed on schedule and combined with poor driving habits, the engine's operational burden will increase, eventually causing the engine warning light to illuminate as a reminder of a fault. Solution: Follow the time or mileage intervals specified in the vehicle's maintenance manual to ensure comprehensive maintenance and rule out non-maintenance-related issues. Fuel Quality Issues: This refers to both fuel and engine oil. The fuel used in cars typically has a specific grade, and engine oil can be semi-synthetic or fully synthetic. Manufacturers usually recommend which fuel grade and oil type to use. If the owner fails to follow these recommendations, long-term use can lead to engine wear, triggering the warning light. Solution: Use the appropriate fuel grade and engine oil as specified for the vehicle. Poor Combustion of Air-Fuel Mixture: Faulty spark plugs, fuel pump issues, or clogged fuel lines can cause poor combustion of the air-fuel mixture. This leads to engine carbon buildup or knocking, which the oxygen sensor detects and reports to the ECU, prompting the warning light to illuminate. Solution: Check the engine ignition coils and spark plugs. Inspect the performance of related sensors, such as the (front/rear) oxygen sensors, coolant temperature sensor, intake temperature sensor, throttle position sensor, air flow meter, and intake manifold pressure sensor. Examine the air filter for contamination—if clogged, it can cause an overly rich mixture, requiring cleaning or replacement (as needed). Check for fuel injector leaks and the performance of the fuel pressure regulator, as malfunctions can also lead to an overly rich mixture. Intake Issues: During combustion, the engine requires air intake, making the air filter crucial. If the air filter is dirty or not regularly cleaned, it can affect airflow, potentially leading to blockages and, in severe cases, triggering the engine warning light. Solution: Regularly clean or replace the air filter to ensure proper intake system operation. Turbocharger Issues: Problems with the intake boost pipes or turbocharger can also cause the engine warning light to illuminate. The most common issue is turbocharger failure, accompanied by symptoms like oil leaks, excessive oil consumption, reduced power, metallic noises, or blue/black smoke from the exhaust. Solution: Visit a 4S shop to inspect and replace the turbocharger. Often, repairs are not cost-effective, making replacement the better option. Exhaust Issues: Faults in the rear oxygen sensor, catalytic converter, or exhaust camshaft and bearings can trigger the warning light. The most common issue is a faulty catalytic converter, which can be caused by physical damage or fuel system problems. Solution: Use lead- or silicon-based lubricants to maintain and clean the catalytic converter. Anti-Theft System: If the car's electronic anti-theft system malfunctions or the anti-theft controller is incompatible with the engine ECU, the engine may not operate correctly, and the warning light will illuminate. Solution: Seek professional assistance at a repair shop, as this issue cannot be fixed individually. Engine Misfire: This occurs when one or more cylinders fail to operate properly, leading to symptoms like reduced power, difficulty starting, or unstable idling. Solution: Identify and replace the faulty cylinder components. If internal mechanical damage is present, a major repair at a service center may be necessary.