What are the reasons for the engine fault light being on when the engine is not started?
4 Answers
Engine fault light being on when the engine is not started is caused by: 1. Poor gasoline quality leading to incomplete combustion of the air-fuel mixture in the cylinder, resulting in carbon deposits; 2. Excessive engine mileage causing weakened spark plug performance; 3. Mechanical aging of the vehicle; 4. Damage, poor contact, or signal interruption of the water temperature sensor, crankshaft position sensor, air flow sensor, intake air temperature sensor, or oxygen sensor. The solutions for the engine fault light being on when the engine is not started are: 1. Clean the engine carbon deposits; 2. Change to higher quality gasoline; 3. Replace the spark plugs. The function of the engine is: to convert the thermal energy of gasoline into mechanical energy by burning the expanding gas in a sealed cylinder to push the piston to do work.
I remember one time when my car's engine wouldn't start and the warning light came on, which really scared me. It turned out the battery was old and dead, and the system triggered the warning when it detected insufficient voltage during startup. Other possible causes include poor contact in the starter relay, a faulty ignition switch, or the ECU receiving incorrect signals such as from an oil pressure sensor issue. That time, I tried several times forcefully, which ended up completely draining the battery, costing me a lot in towing and repairs. Now I've learned my lesson—when encountering similar situations, I call for roadside assistance immediately instead of struggling with it. Replacing the battery every 3 years or so is a good preventive measure to avoid being stranded on the road.
If your car's engine won't start and the warning light is on, don't panic. First, check if the battery connections are loose and use a multimeter to test if the voltage is at least 12V. If that's fine, inspect the ignition switch or relay for signs of aging or malfunction. Sometimes, the warning light is simply the system alerting you to a detected issue during self-check. I've encountered this a few times with my own car—it's often due to a drained battery, so regular maintenance and timely replacement are key. If you can't resolve it, head to a repair shop promptly to avoid safety risks.
The usual causes are insufficient battery voltage or depleted battery power, issues with the starting system such as a damaged ignition switch or starter motor failure. The ECU control unit may also illuminate the warning light if it detects abnormalities like false sensor readings. It is recommended to first check the battery connections and fuses, while more complex faults can be resolved by reading the fault codes with diagnostic equipment.
