Turn off the ignition and disconnect the battery negative terminal
Locate the ignition coil
Inspect the coil for cracks, burns, corrosion, or damaged wiring
Check the coil connector and terminals for looseness or corrosion
Use a multimeter to measure primary resistance between the coil terminals
Compare the primary resistance reading to the manufacturer specification
Measure secondary resistance between the high-voltage terminal and the primary terminal
Compare the secondary resistance reading to the manufacturer specification
Check for continuity between the coil terminals and ground if required by the vehicle design
Test for proper power supply to the coil with the ignition on
Test for proper ground signal from the ignition control module or ECU
Swap the coil with a known good coil if available
Use an inline spark tester to check for spark output
Reconnect all components and clear any fault codes after testing