My daughter has a 1996 Saturn SL with something over 100K miles on it. It runs generally well, although using a quart of oil every thousand miles or so. It passes the smog check required for her registration. It’s had new spark plugs within the recommended period.
Recently she went on a road trip, and hit stop-and-go traffic for a couple of hours in one large city; it being January in a warm climate, the weather that day was presumably neither very hot nor cold. The Check Engine light came on. Fortunately she had the time to take it to a mechanic recommended by a friend local to the area, who pronounced the engine OK. She proceeded without incident for the rest of her thousand mile trip.
Sounds to me like the emissions crossed some threshold beyond “marginal” during the lengthy idling and running at low speed. Question: if we wanted to avoid such a condition, what kind of repair would you expect to be recommended, if we have someone take another look? I guess it’s worth having an idea in advance, in case the recommendation is expensive, so that we can judge whether to bother or not.