How do you know when coils are bad in 1998 Buick century?

You can determine if the ignition coils in a 1998 Buick Century are bad by noticing symptoms such as rough idling, misfiring, or difficulty starting the engine. Additionally, if you experience a decrease in fuel efficiency or see the check engine light illuminated, it could indicate coil issues. For a definitive diagnosis, you can also use an OBD-II scanner to check for error codes related to the ignition system. Lastly, visually inspect the coils for any signs of damage or corrosion.