I have a 1996 850 Volvo with 38K miles. I just bought it a few months ago. I had code 422 which I researched to the 2 O2 sensors not agreeing with one another. I replaced the front O2 sensor and now the car runs rich. I do not get code 422 anymore. I see black smoke coming out the exhaust. I do not get code P172 (running rich) as of yet. I replaced the O2 sensor with a Bosch Volvo replacement ($150). I disconnected the battery for several hours and connected it again. Do you need to replace both sensors at the same time? Any other ideas?
I do not how much if any bearing this will have on your problem but it may give you something to think about and may save you money. I am presuming that you bought the sensor and self fitted it?.
I have a V70 T5 and after a service plus a top engine mount change it went like a rocket. However the performance was due to massive over-fuelling due to the fact that the mechanic left the clamp holding the turbo inlet pipe completely undone. The extra air sucked in through the loose outlet pipe from the air box fooled the sensors into pumping about 50% extra fuel. The consequence was black smoke from running too rich and a code was thrown when the first O2 sensor gunked up with soot etc.
The garage warranted their work and a new sensor was fitted but here is where you may have a problem. The new sensor, and they were the only ones available are re-designed and need the latest software download to work properly. Although I had a sensor fitted in a different model vehicle it may be that Volvo have changed the parameters retrospectively and the new may not communicate correctly with the old without software changes. My software was up to date as it was re-loaded in the last six months.
It only took 120 miles of a loose turbo pipe to finish off my O2 sensor and I do hope that your $150 lasts longer than that.
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