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SOMETIMES a Lazy O2 sensor(oxygen sensor) will turn on a check engine & then go OFF - but SOMETIMES it will SET a Hard Code.U need 2 check the History of codes in the Computer It could be the Thermostat. I had a firebird that had the same problem. Turns out the thermostat was too cold. There is a problem that is affecting the emissions system. There are a multitude of possiblities as to why is comes on and goes off. Whatever is happening isn't consistent and until it is, I wouldn't worry about it. I would make sure that the car is tuned up however and other maintnence is current. See "What maintenance should an Owner do?"

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โˆ™ 2005-10-14 23:24:49
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Q: What could be the problem with a 1994 Pontiac Firebird 3.4L if the check engine light comes on but goes off by itself and there are no scanner codes?
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