Turn off the engine and disconnect the battery
Locate the coil pack
Inspect the coil pack for cracks, burns, corrosion, or damaged wiring
Check the spark plug wires or coil connectors for looseness or damage
Use a multimeter to test primary resistance across the coil terminals
Use a multimeter to test secondary resistance between the output terminals and primary terminals if applicable
Compare all readings to the vehicle manufacturer’s specifications
Swap the coil pack with a known good one if available
Start the engine and check for misfires, rough idle, or improved performance
Use an OBD-II scanner to check for ignition-related trouble codes
Test for spark output with a spark tester
Replace the coil pack if it fails resistance, spark, or scan tests