Hi
Over the weekend after getting tired of looking at that
check engine light that had been off and on for a good part of five months
I decided to try Sin's torching method on my oxygen sensors on my 1996 850R.
Removed both, without unhooking wires and used a regular Propane torch to heat
the ends up till they glowed red, making sure to get some of the flame through
the holes in the tip. After allowed to cool for five minutes i blasted both with brake cleaner, once again making sure to get some inside the tips also using a wire brush to finish some of the sot on the outside off.
Used compressed air to clean out the remainder of the cleaning liquid.

This was meant to be the last resort before proporly diagnosing and replacing
one or both sensors, car has 106K.
To my surprise it seems to be working, the light went out by itself after
running what i have read a complete cycle without detecting any errors.
The car also has got its young powers back and it runs great again.
By the way, the code I had was P172 engine running rich, even though my
gas mileage stayed the same.

Hope this can help someone from having to replace those overpriced expencive
sensors. It only takes 15 minutes so its worth a try.
Regards
Thomas