The triggered code came from a certain condition exhibited by the 02 sensor... that condition is probably based on what "return" the sensor is presenting to the computer... What would be nice to know is whether that is actually going on, or is it a result of another problem that "presents" the same conditions.

I have found that an 02 sensor code was triggered from a vacuum leak. I fixed the leak and now don't have an 02 sensor error... it's now a knock sensor code. Go figure.

The problem with Volvo is the parts and labor are so expensive that "shotgunning" the fix without knowing for sure, is unacceptable. It's sad to read how transmissions are replaced on 850's when it quite possibly could be the Gear Position Sensor i.e. PNP switch. Just depends on the knowledge, accuracy, and/or honesty of the repair facility... Second opinions and excellent forums like this are key to cost-efficient repairs.

Good luck, but be careful...

Shawn