Original to transform the battery voltage to the much higher voltages required to operate the spark plugs
WHY YOU MUST REPLACE THEM;
When it fails, you get:
1 Misfires – The engine shakes, idles rough, hesitates, or loses power. Check engine light with P0301-P0308 codes. That’s the main reason.
2 Bad fuel economy – Unburned fuel from a dead cylinder gets dumped into the exhaust.
3 Catalytic converter damage – Raw fuel from misfires overheats the cat and can melt it. A ¢100 coil can cause a ¢1,500 cat job if ignored.
4 Hard start or no start – If multiple coils die or it’s a single-coil system, the engine won’t run.
5 Engine damage risk – Constant misfires wash oil off cylinder walls with fuel, causing wear.