Why is the light with a car and spanner on?

The light with a car and spanner on is the check engine light. It is designed to alert the driver to a potential problem with the vehicle's engine, emissions system, or other components. The light can be triggered by a variety of issues, including a loose gas cap, a bad spark plug, or a more serious engine problem. When the light comes on, it is important to have the vehicle diagnosed by a qualified mechanic as soon as possible.