Both Huw, and James M. responded with almost exactly the same procedure, which I have already put to practice. My voltage read (after a 15 minute drive) 0.220 volts, steady, no fluctuations for about a minute. I suppose my almost new CDN$130 Bosch replacement O2 sensor is history. I think I will try a different brand at half the cost this time. Thanks again Lino 83 Ur-Q 86 5ktqw