Emissions and Wiring

[brown_almond_eye]

I think Firestone in Tempe is ripping me off!! I've invested way too much into this car. Like most of you, I have dealt with the same problems from the door locks jamming, key unable to turn in the ignition, timing belts (thankfully I replaced that before it ruined the engine), brakes, oxygen sensor replaced, and now the check engine light keeps coming on! It stalled on me twice in the middle of the intersection, can you believe that!! I took the car to Auto Zone and the diagnostic check said it was the emissions and wiring. So I went to Firestone since they were familiar with my car and they refunded the diagnostic charge back to me since they weren't able to find the problem. The reason why I think their ripping me off is because each time I've taken my car in for repairs or oil change, I leave with something else wrong with it. Here's my question: What does the emissions and wiring codes mean? Does that have anything to do with the oxygen sensor..because i had that replaced in January. The car currently has over 68k miles.

Thanks and I look forward to anyones response!!
Belinda