Steps to changing one - pull up passenger side carpet, unplug sensor. Loosen 2 tranny pan bolts, remove sensor wire from hold down clamp. Unthread sensor from downpipe. Reverse steps to install new sensor.

Not necessarily a wear item but O2 sensors do degrade somewhat over time. You may see a dramatic drop in fuel economy when one goes bad, but not if it is only slowly dying. A CO test can give some indication if: you can't get the CO numbers to hold, or if you see a delay in the adjustment of CO numbers in response to changes in throttle. The CO should numbers should adjust and stabilize pretty quickly when going from idle to 2K back to idle. Slow adjustment usually equals a dying sensor.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.