What are the reasons for a vehicle not starting?

[VincentRose]

There are several reasons why a vehicle may not start: 1. Poor quality gasoline, leading to incomplete combustion of the air-fuel mixture during engine operation. 2. A damaged or loose oxygen sensor or sensor connector can cause the mixture to be too lean or too rich, resulting in malfunction. 3. If the air flow sensor or its circuit malfunctions, the ECU will not receive the correct intake air signal, preventing proper fuel control and causing the mixture to be too lean or too rich, which makes the engine unable to operate normally. 4. Carbon buildup on the spark plugs can lead to poor engine performance, causing difficulties in starting, unstable idling, poor acceleration, backfiring during sudden acceleration, excessive exhaust emissions, increased fuel consumption, and other abnormal symptoms.