Hello Keith

Like you I have seen this code many times, which usually ends up getting expensive to fix
Although the vehicle doesn't normally display any other symptoms and will fly through a emission test

For the last 2 vehicles I have seen this code on I used a simple extension to move the Post sensor out of the direct flow of gasses

To do this I used an old style ford OHV Spark that I remove the core and welded to a 18mm 1.5 pitch Nut (2 if you have the room) then weld up the end of the spark plug then drill out to 4mm




This then seems to average the sensor output and so far has not brought back on the lights

Not my Idea just read it somewhere and it seems to work

HTH
Terry