I posted a question the other day about a Check Engine light on my 2001 Tundra. I had a new battery installed at Autozone last Friday and later that day noticed the Check Engine light on. After some suggestions, I went back to Autozone. My alternator tested fine. The code for the Check Engine light was PO155 for an Oxygen Sensor problem. After checking my Haynes repair manual at home, I decided this wasn't a good thing. The diagrams showed multiple oxygen sensor locations. I wouldn't know where to start. I am still wondering if this has something to do with installing new battery. If you leave the negative terminal disconnected for awhile, won't this clear any code for a Check Engine light problem? I'm just wondering if this could also throw up a false problem code. The timing of this with the new battery install seems like too much of a coincidence. Also, my truck is getting older, but it has less than 46,000 miles and I thought these Oxygen sensors would last longer. Is it off to the dealership? Any suggestions? Also, is this a problem I should get fixed in the next day or two or can it wait awhile? Appreciate any help. Thanks.