I just finished spending a total of $2500 in round numbers on my 98 V70 to update the catalitic converter and O2 sensors. This was because I disconnected the battery to repair my ABS system and the O2 codes never reset. I'm told a typical problem at least with the 98 V70. I started with aftermarket cat and O2 sensor. that didn't work. Changed the Cat to a factory one (very expensive). Also replaced the O2 sensor to a bosch OEM but still no success. finally had to replace both front and rear O2 sensors with factory units and have the code flags fall using a Dyno system. This of course cost me $200 to have it done because I don't personally own one.

Recomendation, Anytime you have systems monitored by your computer, use factory replacement components. May cost more but less headache.

Good Luck
Mase
98 V70 136,000 miles, 2000 V70 105,000 miles

On my 850, there is a black (the signal wire) two whites (heater wires) and a gray (ground). From your description of the univ. sensor, I'm guessing the two blacks must be heater wires so you must have the signal/ground wires reversed. My guess is gray is ground so white must be the signal wire.

jB