I just finished installing my rear o2 sensor at 167K! (did the front at 165K)
CEL came back on .
Living in the Missouri salt belt, the nuts were corroded down from 13mm to about 12.5mm! Unwrenchable with standard tools.
I found out some things that may help others.
When you consider doing this, start spraying these nuts and studs with a penetrating lube (PB Blaster, Liquid wrench, etc.) for a couple of days.
1. Buy the sensor on line - got mine for about 60% of what the auto parts store wanted. Denso #234-4189 for the 3.4L v-6 auto.
2. Have an angle grinder handy (or Dremel) for cutting off the 'shield' around the o2 sensor. AND (if necessary) to grind on the frozen nuts.
3. I bought the Craftsman Bolt Out kit - and it was the the ticket to FINALLY get the frozen, rusted, corroded, @#%* nuts off!
4. The replacement nuts are M8 X 1.25mm
5. The connector is located under the passenger seat thru a gromet in the floor.
6. Plug in the connector, running the male end thru the floorboard to the female end under the passenger seat.
7. Install the gasket and new sensor into the exhaust, use anti-sieze compound on the studs and install the new 13mm nuts.
8. by doing this myself I saved about $100 after buying the tool Bolt Out Kit.
9. enjoy the CEL not being on anymore, increased MPG, satisifaction, and if you're old enough, maybe a beer!
I will tack weld on another shield that I will fab out of expanded metal so the water, mud, salt, etc. will not collect around the new sensor like the original shield allowed.