What causes the engine light to turn yellow?
2 Answers
When the engine light turns yellow, it indicates that there is a fault in the engine, which could be either a false alarm or a genuine issue. The reasons for the engine fault light turning on are as follows: 1. Dirty engine cylinders with carbon deposits. Over time, some carbon deposits will inevitably accumulate inside the engine. These deposits can alter the engine's design parameters and are inherently unstable, trapping heat. The trapped heat can cause uncontrolled ignition, leading to engine knocking. 2. The primary reason for the engine fault light turning on is poor combustion in the engine. Oxygen sensors are installed in the engine to monitor its combustion state. If the combustion state is poor, the engine fault light will illuminate.
Last time my car's engine light came on yellow, I immediately went to the repair shop for a check. The mechanic said this usually indicates an issue with the emission system. Common causes include a faulty oxygen sensor, which monitors the oxygen level in the exhaust—if it's dirty or damaged, the computer may falsely report a problem. It could also be due to a loose fuel cap, where gasoline evaporation causes pressure imbalance, leading the system to mistakenly trigger the light. Sometimes, aging ignition coils or spark plugs can activate this light because incomplete ignition affects combustion efficiency. More seriously, a clogged or damaged catalytic converter could be the culprit, which is expensive to fix. If the light stays on and you continue driving, fuel consumption may increase, emissions may exceed standards, and even the engine could be damaged. I suggest first checking if the fuel cap is sealed properly. If that doesn’t work, use an OBD scanner to read the trouble codes or visit a professional shop—don’t delay, as it could affect driving safety. Regular maintenance of spark plugs and sensors can prevent such issues; I get them checked every six months.
