With the ignition switch in the ON or START position, voltage is applied to the ignition coil. Each ignition coil consists of two coils, a primary and secondary coil. The coils are mounted on top of the spark plugs. To energize the primary ignition coils, the Powertrain Control Module (PCM) provides the ground for the primary circuit. The PCM uses the crankshaft position sensor and camshaft position sensor signal to time the energizing of the coil. When a primary ignition coil is energized and de-energized, the secondary coil produces a high voltage spike to the attached spark plug.