CEL o2 sensors | Ford Explorer Forums - Serious Explorations

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CEL o2 sensors


Well-Known Member
May 24, 2011
Reaction score
City, State
Zanesville, Ohio
Year, Model & Trim Level
99 Explorer Sport 4X4
I got my codes checked and they were for my o2 sensors, something like bank 1 sensor 1 running lean and bank2 sensor 2 running rich - any ideas? Also when Im slowing down to a stop I get a bump from the back- kinda like if the universal joint was bad and taking off from a stop. its a 99 explorer 4.0 4wd
DO i have a o2 sensor after my cat? I was wanting to take my cat off since we dont have emission test here so what would I do with the o2 sensor for that if there is one
My battery light also comes on sometimes and the code said corroded terminal or something so I cleaned the battery terminals but it still comes on so it might be the starter connection

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How does it run overall? could be lots of problems

it runs good, needs a new muffler since the one on it is split down the seam though, think that could be the problem?

ok, I went to Autozone and they scanned my codes for me and it came up a small leak in the EVAP system, we found that the EGR solenoid was bad so we replaced it, and now Im only getting the code P1151 which is my O2 sensor running lean, I cannot find any vacum leaks anywhere, does seem kinda weak on hills though, not sure when or if the sensors have been changed before, but it has 208,000 miles on it and the sensor looks like it might have been changed before

O2 sensors are supposed to be changed at some 80k miles. So even if they where replaced at 100k, now they are due again...
But lean condition can be due to other things too (like air entering into intake manifold).

we tried spraying WD-40 all around and couldnt find anything, I dont know when they were last changed or if they have been, I can see what seems to a carbon spray look where it screws into the mainfold, kinda like the exhaust was leaking around the threads