I have replaced all 4 02 sensors in the 1999 volvo s80. i still get a code of p0154 which states bank 2 sensor 1 no activity. bank 1 sensor 1 shorted out against the exhaust pipes. we replaced all 4 02 sensors. the code is still coming up. what else could it be in the 02 sensors to bring up that code, and what do you suggest?

You have most likely a sensor harness wiring problem, no signal return, at this point your system needs to be hooked up to what is called a "break out box" to see what lead is dead, most likely a broken burnt or damaged wire, there is no easy way to do this, I strongly suggest this go to the Volvo dealer for diagnosis or rewire that sensor all the way back to the PCM (Powertrain Control Module), but preform these few checks 1st before you give up, pull the connector off at the sensor and look for pushed out pins in either the male or female side of the connector, you may also want to swap that sensor with the adjacent O2 sensor and see if the code comes up for bank 2 sensor 1, in that case the new sensor is defective, that is rare but it does happen.