I have a '97 850 turbo with 140 K on the clock. I checked my MPG recently and am only getting 20-21 MPG with mostly highway driving. This car came with all of the records from where it had been taken to the dealer for repairs. I don't see that the O2 sensors have ever been replaced. I'm wondering at this mileage if it would be a good idea to go ahead and do so. I'm not getting a check engine light. I usually don't drive it hard, so I was hoping to get a little better fuel economy.

Many thanks,
Dave

I did exactly what you describe on my '95 850 non-turbo with 130,000 miles. Thinking that replacing them might help my MPG, I had both of the original O2 sensors replaced. I did not see any change to my fuel economy after the new sensors were installed. I was getting 22 MPG combined city/hwy before the change and 22 MPG after the change. I would check out all of the other suggestions mentioned first.

If you are into energy conservation (a worthy goal) then it may be a good idea to replace them. If you are trying to save money, then you should calculate the cost/benefit ratio. You might find that it would take 5 or 6 years to break even on the deal, depending on how you drive.

Volvo recommends changing them at 100K. They typically fail slowly so they don't usually set a DTC right away. We had an old Ford (dirty word here) WIndstar that still had the origional O2 sensors when we sold it at 170K so they don't necessarly fail at any given milage

240-740-850

Always suspect vacuum elbows and lines before spending $350 for O2 sensors. Also, make sure your filters are clean, tire pressures are good, brakes are not rubbing (especially the e-brake drums), the plugs are gapped and clean, and wheels rotate freely.
Do not wait for the CEL to come on to check codes. Some codes require another code to turn on the CEL, while some require multiple hits before action is required. Pepboys and Autozone are free.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)