Just had P1646, RH sensor failure. Replaced it, now after about 300 mikes I have P1647 which is the LH sensor. Is it just a bad coincidence or fairly usual that they fail together?

 

Just a coincidence, I had an upper then the lower fail, both for the heater element within a few months.

 

Just bad luck then. I spotted your photo in a similar thread on the uk site, did you get at the n/s sender from above or below?

 

Both pre cat sensors are relatively easy to access from the top of the engine.

Access to the lower sensor from below is very restricted, the gap between the transmission and exhaust is only about an inch and a half.


This picture gives the wrong impression of how bad the access is.





Access was done this way with a wobble on the O2 socket and a couple of extensions.





I first tried it with a 3/8th set up which ended in failure.





So I moved on to 1/2 inch which was able to break it free.





I was able to reach down from the top with my skinny arms to screw the new one back in then tighten from below.