How do you know if a coil pack is bad on a 2004 trailblazer?

To determine if a coil pack is bad on a 2004 Trailblazer, you can check for symptoms such as rough idling, misfiring, reduced engine power, or a check engine light. Using an OBD-II scanner can help identify any trouble codes related to ignition misfires. Additionally, visually inspecting the coil pack for cracks or damage and testing its resistance with a multimeter can provide further confirmation of failure. If the coil pack shows signs of malfunction and the other components are in good condition, it may need to be replaced.