I just recently replaced my o2 sensors. I first did the one after the cat...no problem. A couple of days ago, I replaced the pre-cat sensor and now my SES light is on. I used the same brand of universal 4 wire sensors on both. Anyone have any idea what could have gone wrong?

 

You need to check what code is showing for the SES light. It may be totally unrelated to the O2 sensors. Check the code, then come back and post up what it is. If it ends up being an O2 sensor code, clear it, and see if it comes back.