I have a 99' with the 2.5 and I just replaced all 4 o2 sensors with the cheap ones mentioned on this thread (USOS 4000) and I'm having problems similar to the other guys with the 2.5 engines
Before I was getting:
p0134 (no activity detected bank 1 o2 sensor)
The error codes I'm getting now are:
p0131
p0151
p0137
p0157
and
p1115
p1119
p1117
p1127
The errors all have to do with low voltage and heating on all 4 of the o2 sensors. I double checked the wiring and they match up as they should. The guage of the wiring on the cheap o2 sensors is a lot smaller than the OEM, so maybe that has something to do with why the don't work.
Larez2