Help Please!

Ok Here Is My Problem......I Have A 99 Ford Windstar That Has O2 Sensor Problems.......Have Replaced The One In The Rear And Just Replaced The Front Cause I Was Having A PO155 Code.After Doing That I Still Have A PO155 Code......What Do I Need To Look For Or Can Do To Fix?

Thanks In Advance!

The P0155 code concerns "circuit malfunction on upstream sensor bank two". That would be the "first" (closest to engine) sensor on the front-of-car manifold.

It may be a harness problem however, not a sensor (... but it often is the sensor).

Ok Here Is My Problem......I Have A 99 Ford Windstar That Has O2 Sensor Problems.......Have Replaced The One In The Rear And Just Replaced The Front Cause I Was Having A PO155 Code.After Doing That I Still Have A PO155 Code......What Do I Need To Look For Or Can Do To Fix?

Thanks In Advance!
After the O2 sensor was replaced.. did they reset the CEL.. Or turn off the light.. It wont turn off by it self.. You can disconnect the Battery and reset it that way. If there is still a problem it will come back on..