Toyota Repair: Check engine light on 89 gts corolla, engine misfire, oxygen sensor

Question
QUESTION: I changed the exhaust on my car and wrecked the o2 sensor in the process.  I then replaced the 02 sensor with a denso one.  The check engine light came on immediatly even after resetting the ecm.  I dont think we tugged on any wires but i was wondering it there was any fuses or switches or relays that could have flipped/burned.  It is a 4 wire heated o2 sensor.

Thanks

ANSWER: Did this O2 sensor have to be wired in or did it have an electrical connector which made it a plug in installation? What is the trouble code now? Which sensor was replaced? The one in front or the one behind the cat converter?

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QUESTION: upstream sensor and no it was a direct plug in ( no wire spilcing).  In canada their is just the one o2 sensor before the cat.  The trouble code is still a 21 (oxygen sensor circuit malfunction)

Answer
The O2 sensor is not the problem it is only reacting to another condition,since the light comes back immediately it would point to an open circuit in one of the wires, an engine misfire would take longer for the light to turn on, the computer sees an open circuit in the wiring.