The Check Engine light can illuminate for several reasons. The five most common reasons behind the light include the following. First, a malfunctioning oxygen sensor can diminish fuel efficiency and increase environmentally damaging emissions.Second, a loose, damaged, or missing gas cap can cause fuel vapor leaks, triggering the check engine light. Third, the mass airflow sensor calculates the amount of air entering the engine, enabling the fuel injection system to adjust accordingly. Too much or too little air can disrupt this process, impacting performance and setting off your Check Engine light. Fourth, the catalytic converter helps reduce harmful emissions from your vehicle. If it malfunctions or is stolen, excess emissions can trigger your Check Engine light. Last, issues with the ignition system, such as faulty spark plugs or ignition coils, can cause misfires and be the root cause of your illuminated engine light.