Cel p0136

2003 Ford Escape threw this code a few weeks ago so I put in a new 02 sensor and all is good, for about 3 weeks and several hundred miles. Then, CEL back on again, so I replace sensor again, drive about 100 miles, highway, city, then take it in for inspection and it passes, no problem.

Now, another 3 weeks and several more hundred miles, it's back again. What else could be causing this? I'm not clear on how it can drive for so long, through that many cycles and then throw the code. It runs just fine.

I've had success on this forum looking for stuff about my Ford truck - http://www.ford-trucks.com/forums/index.php

Thanks sammm, lots of good info there!