1. Perform the spark test and identify the malfunctioning cylinder. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [SKYACTIV-G 2.5].)
2. Replace the ignition coil/ion sensor of the malfunctioning cylinder with that of a normal cylinder, and perform the spark test again. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [SKYACTIV-G 2.5].)
If the spark is not normal due to a malfunctioning ignition coil/ion sensor, replace that ignition coil/ion sensor.
It is unlikely that all four ignition coil/ion sensors fail to operate properly. To prevent replacing a normal component, perform the above procedure, identify the malfunctioning ignition coil/ion sensor, and replace it.