A flashing check engine light means stop driving immediately — steady is less urgent

A steady check engine light (MIL) indicates an emissions-related fault that needs diagnosis but is not immediately dangerous. A FLASHING check engine light indicates active misfires that are damaging the catalytic converter in real time — continued driving can cause $1,000-3,000 in additional damage within minutes. Pull over safely, let it idle, and tow if it continues flashing.