What causes 2002 Echo Toyota check engine light to come on?

The check engine light on a 2002 Toyota Echo can illuminate due to various reasons, including issues with the engine's emission system, such as a faulty oxygen sensor or catalytic converter. Other common causes include problems with the mass airflow sensor, spark plugs, or fuel system. Additionally, loose or damaged gas caps can trigger the light. It's advisable to use an OBD-II scanner to retrieve error codes for accurate diagnosis.