Have a 2000 D2. I replaced the RF O2 sensor this past May due to it being dead, probably from all the coolant that passed by when the HG blew, which I repaired and all is well on the cooling front.
My current issue is I get a pending code P0154 for that same O2 sensor, which was fine for several months, but when the check engine light comes on, it is giving me P0150. The codes would indicate a dead O2 I thought, but my ultragauge is showing voltage readings from it, however, it seems to be stuck on the low side ranging from .1 to .335 and never higher. I put another new Bosch O2 in and I got high readings from that one.
I can't find any exhaust or intake leaks and the wiring harness is clean and dry. Nothing seems explain why my ultragauge and OBD reader show voltage but the computer seems to think it's not getting anything.

Thanks for any insight.

 

Try changing the opposite sensor and the two rear ones. If those three are worn out then the computer will show the one good one as bad.

 

I am getting perfect readings from the other 3.

 

Also got P0174 while driving it yesterday.

 

Run sea foam through it for a few tanks, clean your throttle body WITH ACTUAL THROTTLE BODY CLEANER, and replace your MAF. You can get one for ~35 new on eBay. If that doesn't work then it sounds like you're having a fueling issue.

 

have you pulled the plug, cleaned it and add dielectric grease to the connections?

 

You probably got a bad new sensor.
Just replace it.

see http://enginecodemaster.com

for codes

 

Bench tested the O2 and it read fine. Installed back in and scanner shows it getting stuck around .645 volts. Pulled 14.5# intake vacuum and its only showing the lean code on bank 2. Bout to drive it off a cliff!!

 

Have you tried swapping the two front sensors left to right and right to left to see if the problem follows?