When your check engine light is flashing, it means that there is a serious problem with your car that demands immediate attention. The most common reason behind the flashing is an engine misfire, which can cause unburned fuel to get into the catalytic converter and damage it. Driving with a flashing check engine light can also cause serious damage to different engine components and emissions-system parts like oxygen sensors. Here are some steps you should take when your check engine light is flashing:

1. Pull over safely to the roadside and turn off the engine.
2. Do not drive with the check engine light flashing, as it can cause further damage to your car.
3. Get your vehicle towed to an auto repair shop.
4. Have a diagnostic test at a mechanic to figure out what is wrong with your vehicle.

Ignoring a flashing check engine light can lead to more serious and costly problems in the long run.