一些比較菜的車係，一旦發動機亮黃燈，運轉不平穩，obd code會直接了當告訴你幾號coil ／火花塞bad了，換件即可

Google forum:

Engine overheating: When a faulty ignition coil is ignored for long enough, it may overheat, which can cause serious damage to the rest of the engine.

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Over longer miles, you do take a risk with unburned gas ending up in the catalytic converter and poisoning the catalyst, ultimately closing the pores in it. However, small miles driven may not matter.