Engine Codes without Service Engine Light on

Does anyone know if the computer on the OBD II (96 Chev. Lumina, 3.1 engine) maintains trouble codes without throwing the Service Engine light coming on?
My car sometimes runs a little rough but the Service Engine light hasn't come on. I just wondered if the OBD II stores codes for some problems and when it hits a threshold, it causes the Service Engine light to come on. I just thought about the O-2 sensor, etc. The car has 92k miles on it.
Thanks and I appreciate any thoughts on this matter.
David
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There are also pending codes. Not quite enough out of the norm to set the Service Engine Soon lamp.
So yes, they can be read by a scan tool.

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wrote:

Yes, it does.

That's what happened on my 2003 Malibu. Turned out the engine was mis-firing and had a clogged injector.
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